Potential Itenerary - please review (BK to Ankor to Krabi)

Hi all,

So after quite a bit of reading I've come up with a tentative route. I'd really like your input and I have a few questions.

I'll only have 9-10 days for this trip (unfortunately) but here's a snapshot of the itinerary that I'm working on. A few things about me:
-Married, mid 30's, not going for the drinking, the bars, the girls, or to sit on a beach all day.
-Do enjoy culture, great sites, great food, anything bizarre and quirky, scuba diving, motorcycles, hiking, animals, great adventures, massages, and great stories to tell.
-For this short of trip I'd rather spend a bit extra on a couple flights and not end up spending half the trip on a bus/train/airport.
-Angkor Wat is high on my list
-Seeing the stunning scenery of the south is #2
-We want to get a great feel for the authentic Thailand, not just the "tourist resort" Thailand.

So with that in mind, I'm thinking for an itinerary something like:
1. USA to BK
2. Train/bus to Siem Reap - spend about 2 days there.
3. Air Bangkok discovery pass flight (2 legs) to Southern Thailand (Koh Pi Pi, etc).
4. Overnight train to Lompori OR maybe flight to Chang Mai/Bangkok) - depending on how long we end up spending in the south.
5. (optional) Train from Chang Mai to Lompori then to Bangkok
6. Arrive in Bangkok
7. Fly home to USA

I'd really appreciate your input and suggestions and I also have a couple of questions:

#1. I think that the Chang Mai phase is probably unlikely. Is that realistic or unrealistic? Lompori seems like a good compromise. Thoughts?

#2. I like monkeys and ruins and Lompori seems like a good place. Thoughts on that destination? It looks like it could be a good day trip or overnight trip from Bangkok. Worth it? How long would you spend there?

#3. For the discovery air pass, you have to buy 3 coupons (6 max). It looks to me like they're transferable. Is that correct? So the SR to BK, BK to Phuket route will take 2 coupons for each person - 4 total. Can one of us buy 4 and then each of us use two or do we have to each buy the minimum of 3?

#4. How much would you bring in USD for Cambodia?

#5. Is it nice to pack snorkel gear or is it just as easy to rent wherever you go?

#6. Where would you suggest diving in/around Krabi?

#7. How hard is it to use the discovery flight coupons? How far in advance should we book and commit to a flight?

I'm not asking you to answer every question; I realize I've asked a lot, but I'd love some guidance on anything that sticks out to you. Thanks!