Nope. I provided flights into and out of Thailand. Once I included a letter explaining that I was travelling the region so I wouldn't be going directly into Thailand. All the other times I didn't bother with the note.
Yep - When I do it, I am in Cambodia 15-20 minutes. Not even long enough to get a bite to eat. Simple stand in one line to get stamped into Cambodia, go to the next line to get stamped out of Cambodia. You have to do the same with Thailand but in reverse order, obviously.
There is are bunches of people doing it so it's not even sketchy.
I live in Pattay and I take a van to Cambodia. Cost is about 3500 baht and takes about 8 hours.
I recently bought a one way ticket from BKK to KLA for $50, I don't know what a round trip ticket would cost. I believe the 8 hour round trip road trip preferable. After factoring waiting for the return trip, waiting 2 hours before flight, travel to/from the airport, the road trips just makes more sense. Plus I am probably saving the planet.
METV gets you 9 months which is plenty of time to figure out your next step. You will have to leave every 90 days (you can stay 60 days + 30 day extension).