You should refer back to ArM 5 p.97 "Preparation for Enchantment",
to ArM 5 p.98 Talisman Attunement, ArM5 p.99 Instilling the Effect, and for clarification and re-statement, to The Mysteries Revised Edition p. 89
- you open any device by spending a season, and must fill it with the pawns required to open it in that season, limited (by the rules) to 2Magic Theory. If MT is not enough, you can't open it. ArM5 p.97
[i]Saga option - some allow 3MT, but the rules say 2[/i]
Note that an unopened device is not a talisman, nor is the initially opened device a talisman, so you are limited by MT at this stage.
1a) enchant the whole of a single substance device (size * material factor) pawns - poor choice for talisman as too few attunements
-OR-
1b) enchant only part of the device as if the chosen part were the only part. Not a good option for a future talisman, as too easily broken
-OR-
1c) open a compound device, with no more components than Magic Theory score, with a number of pawns equal to sum of all components.
Poor choice for talisman, as you can open more spaces later ... (good choice for small cheap device with lots of spaces.)
-OR-
1D) open a compound device (num. components <= MT), with the number of pawns equal to the highest required by any single component.
Best choice for a talisman - you can get the most possible future attunements allowed by MT, while not requiring a huge MT score just to open the thing.
- Spend a season to turn the opened device into a talisman. Only at the end of this can you use any talisman rules. Stage 1 is not a talisman!
ArM5 p.98
3a) re-prepare it for enchantment, with as much or little Vis as you like, up to total capacity limit of (Highest Tech + highest Form). you can do this piecewise, ArM5 p.98
-OR-
3b) invest a magical effect in the talisman (limited by number of open spaces, etc), ArM5 p.98-99
3c) at the same time at 3a) or 3b) open any one new attunement, from the existing components. (This is why 1D) is such a good option!)
ArM5 p.98
finally
4) cast a spell with talisman - bonuses from attunements only apply when the magus is touching the talisman, and only the highest bonus applies.
ArM5 p.98
Attunements apply to totals to cast Ritual, Formulaic and Spontaneous magic, but not to Magic Resistance or Lab activities. (Hence, do not apply to effects in a device, whether you are investing or triggering them -- only applies to spell casting)
ArM5 p.98
Note when investing devices that any and all Shape And Material bonuses apply, but are limited in sum by MT score./ ArM5 p.99
Phew!
In short - the best way to make a talisman is with a compound device - eg a wand or staff inlaid with several woods, bone, metal or gems, with a total number of components equal to MT score. (Best wait until MT is decent!)
Choose components which will give lots of attunement bonuses later, (and will also give S&M bonuses)
Open it initially as an Enchanted Device, with number of panws = highest single component, limited by 2*MT score
Spend another season to turn into a talisman
Now spend seasons opening as many more spaces as you like: up to 2*MT per season, to a total capacity of (max(Te)+max(Fo)). This you can do in stages - this is the "open partially" bit of talismans.
Note that TMRE also has the Virtue: Great Talisman, which allows you to open attunement bonuses merely by using the talisman, and also to craft in additional components when you increase enchantment spaces - still limited to Number of Components <= MT score, but we assume MT score has increased since Talisman was first made.
As for getting a Verditius to open the Talisman - no way! ArM5 p.98 "you can only attune an item as a talisman if you prepared it for enchantment yourself." ... and "A magus may attune an item with instilled effects as his talisman, so long as he instilled all the effects personally".
Talisman magic is very personal!