You can climb across it?
I'm impressed!

If'n it was me, I'd strip it to the outside framing where needed.
Only where needed, and I'd be real careful about anything that looks like a ceiling joist; it may be a cross-tie to keep things from folding up on top of you.
I did this stuff in a former life (20 years construction, everything from carpenter to site superintendent for a new subdivision, so we're back on topic!).
Work extra safe on old houses where structural integrity can be a little more challenging.
Add new wiring so you can heat/cool it when needed.
Frame new ceiling (if needed).
Insulate
Drywall
Paint
Move all your stuff back in ..

Still hard to get done by others for your given budget.



Make your sound your own!
.. I do not work here, but the benefits are still awesome