Is 12-gauge wire adequate to run into between a 7000 watt generator and circuit box?
No, 12 AWG conductors are not large enough for 30 amperes. 

Powering a structure is a complex task, which would require more details than can be provided in a short form Q&amp;A site like this.  If you need help with a small portion of this project, you might find help here.  As for planning the entire project, this is not the place for that.

My advice would be to hire a local licensed Electrician, even if only for the planning part of the project.