It depends - an Embassy can put a note on a record. I mentioned one on here a week or two ago when Netherlands put a note on sopmeones and other embassies would not touch it. I had a reply from an agent who said that was possible but also alluded to certain embassies wanted a bigger controibution.
Are you sure the Embasy in Cambodia did not add a note to your immigration record for some reason? Might be an idea to contact an agent with the contacts to check this.
You can apply while in the USA - you cannot apply in Thailand so if you did come here you would then have to leave to apply in Vietnam, Laos etc. The same is true of applying for the dependent visa for your kids. Much easier for you to apply for all of it in the USa and arrive with the visas
Have a quick search in the group. There have been a few posts recently about successful applications in the UK with the money not requiring seasoning for 3 months.
Decide where you want to stay before signing a 1 year contract. There,are shorter terms available. Of course you could get Ed if DTV rejected but from everything you have said I very much doubt it would be rejected. You seem the poster candidate for soft power :-) I would not worry. Try and few locations first on the 90 day visit to decide where you wish to stay ie city, beach, islands, countryside.
Jomtien have changed their minds backwards and forwards a few times that I know. Wanted it, then chased away, wanted it after travel, chased away next time lol. At least in Chiang Mai I know 100% it is required after overseas travel. I need to check for domestic travel. Luckily I just message property agent when I return and she does it and sends me the acknowledgment.