Remodels are SO much fun! Even simple ones.
First abandon the notion that anything will be square or plumb.
Next assume that whoever did the work before you had no skills and be very surprised if they did.
Third, dispatch with any ideas you might have that resembles a schedule.
Follow those simple rules and you'll be fine!

Two essential tools for any remodel is a reciprocating saw (i.e. sawzall) and a good oscillating saw. The latter being more handy than a shirt with pockets. Have both metal and wood cutting blades for each.