Hi there,
Wow such a long post where do we start!
I think the best thing to do which will answer a lot of your questions is use the search forum box at the top of the page. Just key in what you want to learn about for example, how to bath etc, and previous threads will be shown for you to read and learn.
Start with the basics, eg, do's and donts, do not use Teflon items near your grey as these can instantly kill.
Then take a look in the diet section, there is a do's and donts list again, find out first what not to feed your grey then read through different items you can to give you ideas on what to feed.
Your grey has been passed around alot and needs to gain your trust, there are lots of owners on here with rescue greys who I hope will read your post and give you lots of advice as patience is going to be the key here. You are going to have to work on the basics before even thinking about using a harness.
I wish you all the best with your new companion, remember read through the sections then give us all a shout for any other questions you need answering.
Welcome to the forum.
Caroline