I've built something similar. A generic API that abstracts away implementation details of many different APIs into a simple set of endpoints. From my experience:
1) What APIs has your team built before that qualifies them to build this?
2) How will you manage changes, bugs, and obscure documentation issues in the APIs that will be made available through you?
3) Will your API cache results from participating parties?
4) What language will the API be written in?
5) Regarding API access security: How will you handle access to multiple APIs for the same client when each API requires a different set of tokens?
6) What kind of security (aside from having an encrypted connection) will this system have?
1) What APIs has your team built before that qualifies them to build this?
2) How will you manage changes, bugs, and obscure documentation issues in the APIs that will be made available through you?
3) Will your API cache results from participating parties?
4) What language will the API be written in?
5) Regarding API access security: How will you handle access to multiple APIs for the same client when each API requires a different set of tokens?
6) What kind of security (aside from having an encrypted connection) will this system have?