Without seeing your basement it's a little hard to offer specific advice. Basements are somewhat hard to design because you're always working around existing conditions and changes to, for example, the location of mechanicals tends to be expensive.

Trying to guess what a prospective buyer may want or need is darn near impossible. If anyone was that good at predicting the future, there are better ways to earn money than designing basements. :-) Generally speaking because many basements alreay feel "small" because of the lack of ceiling height and light, I'd suggest trying to keep spaces as open as possible.

One of the concerns of basement bedrooms is a second means of egress should there be a fire. Many (all?) municipalities require so many square feet of window space to provide an exit. This goes back to designing around existing conditions. While adding a window or making existing windows bigger is certainly possible, it tends to be expensive. So in this case, existing window placement may dictate design.

As for "temporary" or "moveable" walls. Anything can be done but it probably wouldn't be a good return on investment when you decide to sell.

Mike