What did you dooo??? No problem, you can fix it.
This looks just like a typical old frame job. No issues, exept that porcelain knob and tube wiring. You need an electrician to remove it and install new wiring in those areas you can get to for now.
The framing, you can remove the loose stud, it is a nailer for the plaster or Sheetrock. Remove the nails and reattach it. Simple.
The stud that is short , add one on to the leg and attach it with more nails. Usually two 16 penny nails every 16 inches will do. Your not rebuilding the framing, just shoring up what is there a bit.
The plaster at the ceiling can be cut out with a grinder, or a chisel and hammer. It has the wire lath in it also. Just get it so it is straight then fir ir out to the thickness of the plaster,then the Sheetrock will get cut to fit, then add some mud and tape.
Someone framed in a window and covered it up. Not a big deal, just make sure nothing is falling down , or not supported, then add some 2x4s to give it support where needed.
I think you need to take a minute and go to the library for a free book on old ballon framing. Just to get the basics down. It will help in the long run.
That and some more experience.
Which you are getting all the time.
Anyone else want to help the guy out?