Software engineer freelancer here. Started freelancing full-time in January 2017 and currently making a decent living, but not yet the salary I used to make. Another freelancer I spoke to recently mentioned it took him two years to reach his former salary.
1/2) Almost all the meaningful work I've done so far has come from my network. I've also picked up some nice jobs from Slack channels.
3) At this point I mostly work alone. I have a client which subcontracts to me and provides me with a project manager, which is amazing. I also know a designer to which I'll outsource design when I think it's needed.
4) This fluctuates wildly for me so I can't really give a specific number.
5) Slightly less at the moment, but would certainly be able to get and probably surpass my former salary with focus and grafting. However, I try and live a more balanced life at the moment as well as work on a side project, so salary isn't my #1 concern.