What is the proper order in framing the basement walls?
The only reason not to frame everything up would be logistics. If it would be hard to get the bathtub or drywall into the basement because of a framed wall in the way. Cost could be another factor. You would be staggering your project in a possibly inconvenient manner. It may also require extra sets of permits and inspections from the local gov't due to the fact that you'll be framing essentially twice.