Good questions.

1. You will get a very large stack of cardboard. It is a "conjoint" ticket which means that there are separate tickets that are linked together. The tkt is written by a single airline, with all the different coupons in order.
2. You are correct in that each of the subsequent coupons are flexible (given availability). I believe that coupons can be as "open".
3. If you change cities, you will have to have the ticket REISSUED, at which time they will recalculate mileage and assess any overage. They charge btwn $25 and $50 to do it. Therefore, save up all those changes and have them done at once.

I had my RTW reissued in Kuala Lumpur last July--I had booked UA and TG in biz class ($US3700). Decided that instead of going KUL-BKK-HKG (all on TG) then HKG-NRT on UA, that I wanted to go KUL-BKK-NRT (all on TG). They had to rewrite the ticket. I don't think I would have had to get rewritten if I had done something like not changing airlines.

I visited the TG office in KUL--it took about 2 hours (dropped ticket off and came back later to pick it up).
Enjoy--it is fun!