Wow - big questions you ask !!

1. You earn points by visiting websites, trying out offers, and purchasing good through their portal.
2. A whole bunch - many regulars have got over 20,000 miles in the last year.
3. Yes - I use Alaska, but you can also spend them at Hilton, Hyatt and Mariott - American Airlines for a while.
4. Probably - but I don't know of it.
5. This is your most contentious question - MyPoints has it fans and then there are those who have had nothing but frustration. MyPoints customer service can be both great and atrocious. Lots of FlyerTalk commentary about this one !!

Hope that helps !!