Hi Oni,
I believe the UC50 is the same as the ESA50, however I've only had experience with the UC50 form - so this is guesswork, but I can't see anything other than a different name occuring.
For your ID, they usually send a message in your online journal asking you to submit your evidence by uploading via a link they supply - this is what they done for me. You can upload 10 different things at a time, so if you need more, then ask via a journal message. I needed 7 links for 76 documents I had to provide in July.
Chris.
P.S - You can also use the following link to help with what benefits you may be entitled to:
www.entitledto.co.uk/ 
