Longevity Rituals are more like an enchantment than a spell; that is, they share more in common with making a magical item than casting a spell. But they are their own thing; they have their own rules.
Parma Magica is an ability known to Hermetic magi, but the result is not an effect you can achieve using standard hermetic magic. That is: there is no technique/form combination that results in an effect like what Parma Magica does. It has not been integrated into general hermetic theory as of 1220.
A magus can learn supernatural abilities that aren't reproducable via standard hermetic magic, and indeed some hermetic traditions come with such abilities by default (house ex miscellanea often do, for example). There are rules in various splatbooks for incorporating such things into hermetic magic, but in the 1220 setting such things are not (yet) integrated into hermetic theory.
Spell design is based on the effect they have on the world. If a spell is designed to destroy magic it'd be Perdo Vim, regardless of what you were casting it on. Corpus wouldn't get a look in. You could certainly enchant your body (or a glove, or whatever) with a PeVi effect that proc'd each time you touched something, but that'd be done as an enchanted item rather than a spell. Spells, as a rule, either apply their effect once and are done, or apply their effect continuously without any easy 'filters' for their entire duration.
Having a spell 'pass on' its effect within the spell itself is not standard hermetic magic. Some magi can do that, but that requires special virtues and is not part of traditional magic theory.
the divine has been around since the creation of the world; it, in fact, created the world. pre-judaeo faiths have followed the divine in a different form, but not a lot of them. it's worth noting that Mythic Europe was created by God in 7 days roughly 4000 years prior to the time setting. the existence of God is relatively easy to prove in the setting, with some caveats. Angels and Saints show up (and actually manifest) with enough regularity that they're documented, and miracles are a very real and sometimes quite spectacular thing. There's certainly groups within the Order who debate whether God is actually divine or just a really powerful faerie, but by canon setting they are wrong; God exists and is all powerful.
It's worth noting also that there is a difference between God and the Divine realm, just in the same way that there's a difference between Demons and the Infernal realm. While God himself is indeed all-powerful (he literally ignores everything the players do to stop him), God's agents are not. Angels might be powerful, but they have might scores like most other critters. God also pretty much never gets involved directly in anything; the closest you come to direct Divine intervention is miracles. God himself never shows up; unless your Saga is going to feature the Second Coming...
Hermetic breakthroughs are anything that significantly changes the rules of hermetic magic. Adding a new range is probably not a hermetic breakthrough, unless it also seriously bends the rules of one of the limits or similar. Hermetic breakthroughs aren't limited exclusively to the 10 limits, but you're still looking at things that have a similar magnitude of effect. For example, working out that all four elements can be treated as one and essentially inventing the art 'elements' that works as any of the four elements (aquam, auram, ignem, terram) and then integrating it into hermetic theory such that a season of you teaching magic theory is enough for the student to start using your new 'elements' art would be a hermetic breakthrough. A canon example of this is Conciatta, who compressed what were essentially four arts (vim:divine, vim:magic, vim:faerie and vim:infernal) into a single art (vim).
Yep. See the Rego Mentem spell 'Exchange of Two Minds.'
Note that voice range isn't a limit, it's simply a range. I'm personally a big fan of having a bevy of sight-range combat spells; they're only one magnitude higher and they get rid of that pesky requirement to make lots of noise. They also work when you're hiding in a storm cloud at 4000' altitude with 'eyes of the eagle' and 'clear sight of the air' active.
The main thing to remember, though, is that each spell typically does one thing. If your spell starts looking like a swiss army knife with a half-dozen requisites, it probably wants to be two (or three) different spells each with clearly delineated results.
If I wanted a spell that, when my grog tocuhed someone, cast dispel magic on them, then I'd start with a PeVi 'dispel' effect, then I'd develop a whole new MuVi 'transfer control of spell' effect and another MuVi 'alter target of spell on the fly' spell...
The problem is that starts looking unnecessarily complex, so I'll likely scrap the whole project and just develop a voice-range or sight-range PeVi spell and be done.