Learning About Proxies

Hi all, I have a few questions about proxies that I can't seem to find the answer to on Google.

When going through a high-anonymous proxy, your traffic is still transported in clear text. So if i were to gain access into a database on the other end, what is being read by me, can also be read by any of the proxies that I am going through, correct? Is there some sort of encryption along the way that would encrypt the data and prevent proxies from easily reading it?

Also, if i were to setup my own proxy, what tools are helpful in acquiring passwords, pictures, video streaming data? Would cain and abel be helpful?

Any information is appreciated.