I have yet to figure all of this out. I just joined Steemit a month ago. I am not in it for the currency (though earning rewards beats Facebook that you can't take to the bank), but I just like to get my posts out without getting censored (Facebook just locked me out a few days ago - https://steemit.com/facebook/@thermoplastic/wtf-facebook-i-am-royally-pissed-off).
PS: I don't even know what a "Witness" is, lol. The ones I vote for (and often resteem) are usually fellow artists that I either found here, or had known from Facebook before, and some are personal friends also.