I assume the type of mirror does not matter too much. The Leadworker virtue specifically mentions using lead on the rear of the mirror, so they must have existed and been common enough for Magi to access. The lead is for the mirrors and also making the "named tablets" which form arcane connections.
The three uses I have in mind for mirror are:
the spell Face in the Mirror, which is for communicating at speed and allowing a ghost to possess you,
Using the image of a person as a sympathetic bonus for spells, and having that image "locked" via Ring duration so that I always have it. Like taking a photograph of somebody so I have a Pen bonus.
and binding a ghost into a mirror with ring/circle etc. This way they can be bargained with, or released easily.
I doubt I'd use more than a few a year, and would re-use materials too by muto effects. My plan is to create ACs to anyone of significant interest/opponents.
Is it possible to instill multiple effects in a talisman in a single season, in the same way that multiple spells?
Assuming it only grants one shape and form bonus for the season?
Meliai winds up with 348 LP of apothecary ingredients at the end of her 6 cycles, which she could (and presumedly would have over that time) converted via simple spells to 348 tonics of gold. However given that she is addicted to magic, I would assume a number of these have also been consumed during this time (to recover from spontaneous magic), unless this is supposed to simply be what is left over after she was able to gain much more over time... thoughts, ideas, opinions?
May I suggest saving a few to make ligatures? Most of us should have a skill high enough to provide a nice bonus could use some apothecary LP. Haestus should e ale to consistently hit a +2 ligature and he could help support others if they want to dabble.
I haven't "used" the free crafting seasons of work by a skilled craftsman in my character development. Can I save them as an add-on to the BPs from the special seasons?
Or are there suggestions for what to use them for?
Depends on what you are going for. Ships would obviously be useful, but it would be a bit odd to be getting those in cycle 1. Given what I see of the character jewelry might be a good selection, and give him a reserve of items that can be useful for trade or enchantment. At minimum you should probably have a season or two of professional jewelers making your physical talisman...
Technically people have been using the talisman adventure to justify getting the rare parts for a talisman (like a diamond, or ruby), and then using a season of work to have the actual talisman created.
A further note on this. I've been reading the section in Art & Academe (p124) which details what the construction time is for various items. Everything generally takes at least a season to construct if it is to have artistic value, and much more depending on grandeur and size.
For Constantine's talisman I've opted to have the construction done just before the enchantment and attunement, so it has a nominal Aesthetic Quality of 16 (cycle + 10). According to A&A that is two seasons to build. I'm not overly fussed with that overall, except that it technically means that other crafted items are unlikely to have any artistic merit or beauty if they only took a season to produce, or were crafted earlier.
Is the troupe in support of this, or are we eschewing the guidelines for crafting artistic merit for talismans?
I've found that in general the art rules don't work for anything beyond itself meaning that it doesn't play well with the crafting rules from C&G. I'd suggest using the A&A rules if you are making just art, otherwise the C&G rules seem a lot better. Do you have a mechanical purpose for your talisman to have an Aesthetic Quality? If not I'd suggest handwaving it. After all any crafted item does have inherent beauty even if some random person declares it "not art".
Technically a crown or jewelry would have aesthetic quality having no practical use, however that is irrelevant for use as a talisman (unless you want to use the Aesthetics bonus from the common magics sub Rosa article...)