[JThiessen]

Doors - there is not really a way to solve the situation you have, other than to purchase some replacement doors. Are yours painted, or stained? If painted, it gives you a few more options. You can often find those hollow core doors on Craigslist really cheap. If you do buy some, make sure you know which way they open when you look at them (in swing, right hand or left hand...)
If you dont replace them, at least make certain you paint or seal the new cuts somehow to prevent swelling from moisture.

Concrete - Jackhammer....very fast, concrete saw, very nice cut. Is there rebar? If so, you'll have to cut that too. Concrete saws do NOT like metal....

Bathroom.....he, he, he.....! I'm knee deep into my last bathroom remodel. I actually relocated ALL of the fixtures, so I had to completely redo all of the plumbing, including the vent lines. If you hire a General Contractor, he will sub out the plumbing. Or you can act as the GC, and hire the construction guy, the plumber, electrician, flooring, etc.,. I think 5K is sporty given what you stated needs replacing. I have that just in materials for ours ($1K just on the two stinkin faucets...!), and I've done all of the work. I found a book at a local plumbing shop - it was akin to Plumbing for Dummies, but it helped me a lot to know what code's and such I had to meet. Other than that, it was a matter of figuring out where to run the lines to both meet the slope requirment, and avoid other structural items. Since it sounds like you are just "replacing" stuff, I'd say that is EASY......but, if your not comfortable, then sub it out.