Well, unless the SUB-floor is in bad shape, you needn't rip it up. ALl you need to do is find the joists and SCREW the sub-floor to them.
As far as replacing joists/cross-members, you really didn't say WHY you want to do all this demolition. So, I'm gonna hold off on my 'assistance' re: replacing/sistering your floor joists until I hear more. (I'll assume you decided NOT to rip up the sub-floor if you don't post back w/more info.)
For now, my best to ya and hope this helps.
Jay J -Moderator
PS: Also, what kind of finished floor are you going with? Hardwood? Carpeting?