Well..got the Ajax issue fixed (just uploaded my backup file from 1.5.4 and never got the errors again).
Never did figure out the blank pages issue though, unfortunately. So I had to downgrade back down to 1.5.4 and uploaded the backup of my original site.
I think I'm going to wait until I've made a few sales then just pay someone who is a lot more skilled with this to do the upgrade!
Usually I can follow steps fine and get things working but not this time haha.