Usually crown mouldings are not a big thing in contemporary spaces as for trim and baseboards I keep them really simple in fact I love no baseboards but hard to do with most contractors so second pic more realistic.

I would still use a little detail on the moldings. I love the ceiling molding in the first picture. Still has the clean lines but extends to the ceiling. Maybe a taller baseboard with a simple bevel.

you should never rely on your contractor to make design decisions unless you have worked with him previously.

have you already put in the drywall and flooring?

I hope that the contractor did a good job at making the floor and drywall as even as possible.

depending on how even the walls and flooring are, you may have no choice but to let them dictate the dimensions of your baseboards and crown.

typically, a contemporary modern home will have minimal to no crown, baseboards, trim, etc.

here is a discussion that may help educate your contractor about what is necessary to achieve what you want.

http://www.eichlernetwork.com/content/no-baseboard-how-achieve-look

however, given what you have said about your contractor, you may have to uses baseboards, molding, etc. if you do, then just remember to keep the molding, etc very simple and not bulky. I would also not paint the walls, molding, and crown the same color. you could paint the doors a different color.

as for doors, use slab doors. good luck!