Welcome back to the USA. I wouldn't even buy now, just get a job here, work 2 years, then you can probably apply for a loan. A lot of local agents will tell you to buy now because they want the business. But in reality, we are still screwed up. Hold off.
Instead of buying a book, you need a Realtor! A Realtor will help you choose the right lender for your needs. These questions that you are asking are better suited for a lender to answer. But why just trust any lender? Choose a Realtor that you trust and trust her/him to take care of you with quality referrals. You have a lot of questions, and you should. This is a big purchase! But especially since you are a first time buyer, you need to make sure that you are covering all the basis. It is my experience that the hardest thing for a Buyer to do is talk to a lender. It really is a 15 minute phone call and if you decide you don't like that lender, you will choose another one. You should always be able to have a consultation with a lender without paying anything. There are lenders on the internet and TV that seem great but I caution you on choosing them.
To answer your question: It is my experience that a lender will choose the middle FICO score and if you have over 620, you should be able to get a loan. Your time is limited to look, choose, and get closed before the $8000 tax credit time limit. One lender I like is www.innovativemtg.com. They have lots of answers on their site plus you can even do live chat.
Hope this helps, Mark. You can email me if you have more questions at email@example.com.... more