CB750 bobber build... gonna need help!

Any tube meant to fit that model will be fine. Going up from a 16" to a 17" will make the bike handle better. When doing that swap you will be going from a tire with tall flexi sidewalls to a tire with shorter, stiffer walls which will help cornering. Overall tire diameters will pretty much stay the same.

My stock spokes on a '78 cb750k are 18r/19f and it rides awesome. I'm also not planning on dropping it in the back like you are. They do make a 16r spoke for cb750's (I had one and switched it); check ebay as they come up there alot.