Originally Posted by Andrew R Stewart

I would reach out to the instructor and ask if they offer fitting or design help too. If they use a specific design program (and if so perhaps see if you can play with that prior to attending the class).

There are a number of books (some available on line) that sort of cover the writers' views of fit, geometry and materials but we don't even know which kind of bike you seek, most books seem to focus on road/tour riding.

Many do as you suggest and copy a known bike and just alter the fit numbers to suit, the steering geometry remaining basically the same. Others are OK with experimenting more than some and will try out geometry they have wondered about.

Whatever the design I would not place too much importance on this potential frame being "perfect". Between the mistakes you'll make on your first, construction and design wise, and that you will also change over your years I suspect there will be more bikes in your future. Andy