My recommendation would be to start with a smaller bird.
Macaws are great bluffers but there are times they're not bluffing. They can produce a pretty crushing bite that can shatter your confidence in handling them. The key to parrots and being bitten (and you WILL get bitten) is to not take it personally. Blue just chomped into my hand pretty hard and slightly broke the skin. She doesn't hate me, she's just having a bad day and I ignored her warning. If I would have backed off when she told me to, I wouldn't have gotten bit. So essentially, it was my fault.
Walking new foster parronts through how to deal with problems was tough. You're going to have your patience tested. You're going to have your feelings hurt but you're also going to have some of the most rewarding moments when you witness a breakthrough. The people on this forum, I've come to find out, are not only very knowledgeable but helpful as well.