If you're wife is super wealthy a visa to the US should not be a problem. Otherwise, forgot it.
You're in an interesting situation actually.. If you're sure you want to marry your GF, you may want to consider marrying her in the US. I *think* a fiance visa is easier than a wife visa. I *think* with the fiancee visa the US government looks at your financials and such, with the wife visa, they look at hers, which is a little trickier because US government officials are not familiar with Thailand's customs and such.
Many people in this group discourage it, but I have had good luck with it... You can apply for a marriage eVisa online, from Washington DC (or whichever embassy serves your home state). Once the visa is granted you will need to do a border bounce to activate it. For proof of nationality use your passport, for proof of residence use your driver's license. I have done this a few times, a few for marriage visa and a few for tourist visa.
All that being said. I asked an agent once, how much was a retirement visa and how much for a marriage visa... 15,000 retirement, 65,000 for marriage visa. I have known a few husbands who could get a marriage visa but the choose different visa options... The marriage visa can be a pain in the ass depending on the immigration department that serves your area.
People discourage it, in this group, but I have had good luck getting eVisa while in Thailand and doing a quick border bounce to activate it. Otherwise, you will need to go to a different country apply for a different visa, wait there until it's granted, then return on the new visa. Probably some agents can help you figure-out the quickest options.
I have "appalling English grammar and spelling!" and I taught for a couple of years. I did a crappy job but I doubt my students missed out on anything. Teaching in government schools doesn't require you to teach (all students will get passing grade, regardless of merit), it simply requires you to baby-sit, make sure the students don't hurt themselves or the property, and look like a teacher -- that is all that is required.
I have been here 10 years and I know maybe 10 words in Thai. Knowing Thai isn't necessary but probably there are benefits. Personally, I find it better that I don't speak Thai when the police pull me over. It seems they don't really want to take the time to try to explain stuff in English, so the bribe remains pretty low. If they could explain that I needed to pay more for this or that, I might have to pay more.
When I came, 10 years ago, one-way ticket cost about $800. You could live in a template and eat rice... That is the cheapest way.
You have 6 years. In that time I would focus more on finding an income more than finding discounts.
Some younger people come here with the intention of working for a living. I think minimally skilled expats earn about $1000 - $1500 a month, teaching or scuba instructor... Those are pretty much the only two jobs you can do, unless you have some very unique skills (doctor specializing in something and you are recognized as the worlds best, they may let you practice your specialty - but I have not yet seen that).
$500/month gets you pretty good place in Bangkok near no transportation. 750 may get you a decent place near transportation.. Or ride a motorcycle... If you are ok with eating only rice you can probably survive on a dollar a day... Then everything additional costs more. I think you will find $1000-$1500 is enough to get by for awhile. You will have to choose, air conditioning or save for emergencies. You will not have enough money for both.
My advice to you.. Save every penny you can for the next 6 years and/or spend the 6 years finding a job that can be done remotely, or spend the next 5 years acquiring the skill you need to find a job that can be done remotely.
Craigslist and bahtsold.com are good sites to do some rental window shopping.
Over the past weekend I had to re-stamp in (border bounce).. I went to Cambodia, stayed for about 3 minutes and came back.
Thai immigration (and likely the neighbors) are happy to welcome tourists who come to spend time and money, then leave. That sounds like that is what you are doing... I don't think you will have any problems.
If you get pulled aside at an immigration check-point. Make sure to complement the culture, people and food. Some people get this part twisted. If you become argumentative the Immigration Officer can deny you entry and be a pain in the ass... If you are polite and respectful the Immigration Officer is all to happy to grant you permission to stay (and spend money). No kidding, people do get this point twisted.