Welcome TRM! Glad to have you aboard.
We've been thru the stuff you're considering now. And as NZ says, it can be fun in itself.
Probably a good starting point if you are interested in accessories like cutters and such, is Dougie's 59 page article on VII mods at the AMP library: PDF,
http://amp.rokket.biz/lib_uboats.shtml (last article, bott pg). It lists about all the mods ever done to any VII - you should be able to fin at least some potentials or ranges to further narrow down.
You're right about some handful of famous boat flooding the interloobs with info, and almost nothing on many boats. But you can get "implied" info on other less documented boats. eg., my boat U 557, was because of the book Iron Coffins. At the time, there were NO pix of 557. (Possibly one, but it could have been any VIIC - after finishing the model a handful of pix appeared...aaarrrrrgh!). So I went with some info on 556 and famous 558, because they were all laid down at the same time, and 557-558 were real sisters, 30 day difference. (Therefore what 558 had, it was likely 557 had). So if you find a boat with little known, there still might be a way around things.
Have you thought about a VIIB? a few folks have changed VIICs into Bs very successfully.
Hope this helps, keep us posted about your logic and choices. We'll find the right one for you!