I can speak to the 2nd question. The one thing that Americans really get shafted on is "global income". The IRS doesn't care if you don't live in the US anymore, they still want to see a tax return.
When I left Canada a number of years ago, I simply filed a tax return that said I left. I haven't filed one since.
Not so if you're an American. You need to keep filing each year. The good news is that the US has tax treaties with most developed countries, so as long as you're paying as much tax as you would if you were working in the US, you won't have to send a check to the IRS. For example, if the tax rate in your new country is 40% and you would be in the 35% bracket in the US, you will owe no US taxes.