For those wanting to develop new cartridges, is there a single point of access for a knowledge base that keeps reference material for address locations and signals used by existing cartridges?

As an example, say I want to develop a cartridge X but I want to be able to use it with cartridge Y at the same time via port expander.

1) How can I find which signals (like /GAME and /EXROM) cartridge Y uses?

2) How can I find which I/O lines are used for mapping base memory locations like $de00 and $df00?

3) If cartridge Y is only using memory locations $dx00 - $dx0F, where do I find that?

4) If it's only using $df00 - $df0F, will accessing $dfx0 - $dfxF (where X != 0) interfere with cartridge Y's functionality? Basically, will reading or writing other locations access undocumented or typically unused registers and cause erratic behavior?

I think such a cross reference in a single location would be extremely handy for designing cartridges to be compatible with each other. If there isn't one, what would be the best way to start one and where would be the best place to host it? More importantly, is anyone interested in working on this?

Sounds interesting! Setting up a database and throwing down some php code for that shouldn't be too difficult. Perhaps a project for http://codebase64.org ?