Yes, but that's like saying Diameter is terrible because I want it 5 minutes after I cast it. There are a few big things here:
Yes, which is why this is canonical. Look at LoH p.65, noting this:
Maintain the Caster's Spell (p. 65): Add the following sentence at the end of the description. "This effect was invested in Fortunata's Talisman, and takes advantage of a Talisman's closer connection to the maga who created it. It cannot be used by any other magus, although laboratory investigation does reveal its existence and nature."
Note that the erratum doesn't really change anything. Rather, it explains that the LoH effect is correct.
Well, just to play the devil's advocate, what if you make a version of the spell that specifically helps you ignore the pain from spellcasting? In that case, you need not make concentration rolls to maintain it while spellcasting (see the last paragraph of Concentration, ArM5, p.82).
Also let me point out that, as a SG, I would probably not allow Endurance of the Berserkers to reduce penalties from Painful Magic: the rationale being that EotB makes you act as unwounded and unfatigued, but says nothing about pain - and we know that pain from Painful magic produces a penalty cumulative with that from fatigue and wounds.
Thank you, everyone, for the warm welcomes.
I wanted to add to my earlier comments. I have played several RPGs over years and am enjoying Ars very much. I don't mind a challenge to playing a character and look forward to playing this character to its potential. I like the fact he learns very quickly with the lab rat virtues (Book Learner, Free Study, Inventive Genius, Puissant Magic Theory*) just looking for ideas in dealing with the painful magic which so far has only been an issue while I'm out on adventures.
As I'm still learning the game and we've only played 4 ish years of game time so had limited time to grow the character.
Int 5
magic Theory 4
Virtues: Affinity with Creo, Affinity with Corpus
Arts: Creo 12, Rego 9, Corpus 13, Ignem 3
Spells:
Awaken the Slumbering Corpse
Charm Against Putrefaction
The Chirurgeon's Healing Touch
Lifting the Dangling Puppet
Revealed Flaws of Mortal Flesh
Image of the Beast
Whispers Through the Black Gate
Pilum of Fire
BIND WOUND
GENTLE TOUCH OF THE PURIFIED BODY
I was thinking of going hard into longevity potion specialist but not sure how much fun that would be to play.
Thank you all for your suggestions and guidance.
I assume your main problem is casting your Pilum or Fire and Lifting the Dangling Puppet, when you need to deal with enemies.
This is one case when you're better off spending time in lab either magic a lesser enchanted item, if you have the vis, or making some charged items, to bypass the need to cast the spell yourself, or at least, let you rest between castings.
I like this character, there's a lot of potential there.
I think the first and foremost decision you should make is "what type of "grown up" version of him would be fun to play - crucially, not just for you in isolation, but for your troupe as well in the context of your saga. Do not worry too much about "power" in this regard: magi can become really earth-shaking at whatever they set their mind to.
I shall explore a few potential directions of growth, below, starting with the "longevity specialist" you mentioned. I will not look into Mysteries, original research etc. because even with vanilla Hermetic magic there's a whole lot to have fun with.
The longevity (and health) Specialist.
Directions of short-medium term growth:
a) boost Creo, Corpus, and Magic Theory (it's really important, because it allows you to handle the necessary vis - Puissant MT is a good Virtue).
b) Establish relationships with patients, and sources of vis (which might be the same). Remember, if you are good at Longevity, you might work for a patient once in a decade, or even once in a century ... so on the one hand you might charge that patient outrageous prices (in vis, books, lab texts, favours, magic items ...), on the other hand you need to look well beyond your covenant to establish a sufficiently wide base. You could work for other magi, for nobles etc. Ultimately, it's much more of a mercantyle endeavour than one might imagine, and you could be able to obtain magic completely outside of your specialty in the form of magic items traded for your services. This obviously requires your SG to be onboard.
c) Find synergies for with other interesting magics. The most obvious are CrCo healing rituals (including ones to stave off aging crises), and CrCo characteristic-boosting rituals. You will probably have a lot of vis at hand from your Longevity work, and you can put it to good use ... and earn even more. And of course Painful Magic is no hindrance.
d) For adventuring, I would suggest to just forget Pilum of Fire and rely on grogs to do the heavy lifting: with a high Corpus score, and even a modest score in Muto/Rego, there are a lot of spells you can pre-cast on them every day, or every Moon, to enhance them -- making sure you have all the time to recover from Painful magic. Turn them into giants! Make them more robust! Grant them the night vision of an Owl or the the sensitive nose of a hound! Disguise them! Many of these effects are best developed as spells, because they often benefit penetration, so they will "grow" with your character.
Some of them can be really low level, so you need not learn a formulaic spell - just cast them as non-fatiguing spontaneous magic (fatiguing is bad, because you can botch). Have fun collecting all the little bonuses that can help you in this regard, from a talisman with a good corpus S&M bonus, to ceremonial props. If and when you bind a familiar, you can put similar effects in the bond, and they will constantly "enhance" your character without warping him.
One very, very useful effect, that I would suggest developing early on is The Seven League Stride (or variations with R:Touch and perhaps T:Circle), as it allows you to get out of a sticky situation, as well as move around really effectively.
The Cr/Re/Mu/An/Co/Vi "semigeneralist".
Since your character lacks a focus, you do not lose a lot out to trying to expand the breath of your abilities. These three Arts and Techniques together offer really, really a lot of possibilities.
Directions of short-medium term growth:
a) boost Animal, Muto, and Vim. Note that by being "broad", your Art scores will be comparatively lower ... which means excellent books on them are much easier to find! It should not be too difficult to quickly raise everything into the 10-15 range, and eventually into the 20 or so.
b) Play out all the possibilities, noting how virtually all these choices allow for "pain recovery" after casting. CrCo for healing (and in the long-term, characteristic boosting too). ReCo for movement, and to animate corpses. ReAn for movement (that's what you use to turn a wool carpet into a flying carpet). Cr(Re)An to create animal minions that obey you (my favourite: a swarm of bees). MuAn to enhance them. MuCo(An) and plain MuCo for shapeshifting (including disguise). CrAn or ReAn, to create all sort of useful tools of leather, wool, bone, silk. You need a decent Finesse for this, which incidentally will help a lot with Certamen - a magical activity for which your breadth makes you well-suited, and that is unaffected by Painful Magic. ReVi (and this is really important) in your talisman, to keep "dormant" a number of pre-cast spells - so you can "prepay" the pain and unload them when you need them; to extend their duration from D:Conc to D:Sun and D:Moon; and to create Arcane Tunnels that effectively allow you to transform R:Touch spontaneous spells into stuff with R:Sight or R:Arc. ReVi to summon and control demons spirits. ReVi to cast the covenant's Aegis - someone has to do it! And of course, MuVi to perform all sort of metamagic shenanigans that boost your somewhat weaker magic. I have probably forgotten something, but there you are 
c) The most useful things to acquire early on will be strong Summae in the six Arts, plus possiibly a handful of tractatus; and anything to boost the lab total for learning spells and/or enchanting items, compensating for spread-out Art experience (but Puissant Magic Theory and Inventive Genius really help here): lab texts (discuss the availability of these with your SG), laboratory enhancements, a familiar in love with Magic Theory (again, also great for having non-warping Corpus enhancements "always on"), an apprentice.
Note that this is much more of an "adventuring" magus than the longevity specialist. He can still rely on grogs, or slug it out alone - the latter particularly for "stealth" adventures, for which he is really well-suited. He won't be scary-powerful, but I think he can be immensely versatile and enjoyable to play (we had a similar mage in a past saga). This magus can make life very easy for your SG, in that he can accomodate lots of plot ideas, and synergize well with other PCs -- make sure you negotiate for something in return ("I... really envision him finding his True Love, you know")!