You can pretty much put them wherever you wan t to, the only thing to keep in mind is the extra work Involved in moving pipe work to suit the new positions.

The answer to that question will depend on where the entry door is - If the door is a short wall, opening it would create clearance problems for the toilet - think knees. If the door is centered on the long wall the putting the sink in the middle makes better sense since the toilet would be less visible from the door.