Shifting work to your players is definitely an option, but it is also worth getting a rough feel for what the covenant is going to want/need based on its role.
My recommendation:
Get each player to pick a hook they think sounds fun; as in it exemplifies the kind of stories they would like to see in the covenant. Get them to pick a boon as well. Boons really are the opposite of hooks, they describe the kind of stories the players don't want to adventure to solve.
Example: Poverty means 'I want to participate in stories about struggling to survive and the hard choices involved therein' while Wealth means 'I don't want to have to worry about mundane resources.'
With BP, it's worth getting a rough idea of how much is library, how much is vis, etc. But you can honestly play fast-and-loose with BP; as soon as play starts, they become pretty meaningless anyway. People will trade, hunt vis, lose things, gain things, etc.
The library is often one of the biggest chunks of work. My recommendation for a mid-large library is this:
- pick one of the library 'sets' from the core book, deducting the appropriate BPs.
- have the group work out what the summae are; which arts are the good ones, etc.
For tractatii and for lab texts, leave them undefined aside from a few basics (Aegis level 20, Wizard's Communion 20). When someone wants a lab text or tractatus on something, have them roll a stress die and, if the roll succeeds, they find the appropriate text. Add it to the library, deduct the requiste 'amount' of tractatus or lab text points from the pool. If the roll fails, they couldn't find it this season. Doesn't mean it isn't there, just means it was misfiled or something. That way you don't have to track what isn't in the library, only what is.
For Wizard's Communion, my recommendation is make it a level 20 spell, but instead of a default 'at 20' version, go with an 'at 10' version of sun duration. It's the minimum required for decent communal ritual casting.
For difficulty targets, my suggestion is:
spell from core book: 3+
spell from non-core book: 6+
spell I made up myself: 6+ - 9+ (depending on the weirdness of the spell)
spell based on a mystery cult or virtue requirement: 12+ or higher, or maybe simply unavailable
spell of over level 50: 9+ or higher, or maybe simply unavailable
tractatus on an art, arcane ability or academic ability: 3+
tractatus on a supernatural ability: 9+ or higher
tractatus on any other ability: 6+
This is totally house rule, but it works great if you just want to delve straight into play without spending hours working out exactly what is in the library and also ensures the library contains mostly useful spells. I say mostly, because you can guarantee that people will look for stuff that turns out to actually be a bit stupid.