Can I make a bootleg track and release it for free as a download?
Is it legal to make a bootleg track (cut and use my own stems from an existing track to remix myself), and upload it to soundcloud with a download link for free?
Is it also legal to play a bootleg track that an established producer has made, to a crowd if they had offered it for free download?
Thanks for any help you can offer!
Do whatever you want. I do.
What do you think is going to happen?
Honestly - what is the absolute WORST thing that you think could happen?
Check out my Soundcloud. 
If you are a high profile DJ/producer and the label or person who owns the rights to the original notices your track, they could send you a cease and desist order or claim copyright infringement on soundcloud on the grounds that you are promoting yourself with their intellectual property without paying them. That has definitely happened. The latest I can remember is with Julio Bashmore. But if you are a local guy with a couple hundred followers or less, I guarantee they will never bother with it and I can’t remember anyone ever getting sued or fined in anyway for a free d/l. The worst that will happen is that you will have to take it down.
Technically the worst is that you can be sued and forced to pay, even if you didn’t make any money off it. Making it free doesn’t matter at all.
Realistically, that will probably not happen, but be aware that it is a possibility.