I have gotten residence certificates with tourist visa for purposes of banking and getting my drivers license. I think you can get them with tourist visas. Its just a piece of paper that says the Immigration Office knows where you live. It's not an actual residence certificate that you show other countries to establish Thai residency. Its only good for internal Thai stuff.
Koh Lipe is one of my favorites, I believe that is consider "south". Koh Samui, Koh Tao are good second choices, I think those are NOT considered "south". Koh Lipe is difficult to get to, from Bangkok, 1 hour plane, possible sleep over, 4 hour bus, 2 hour boat, and then you are there.
Krabi is a great place because most everything is near. There is the tourist part of Krabi (Ao Nang) and also there is the authentic Thailand (Krabi town). But it's small so you will likely get your fill in one week.
I have applied for and gotten the marriage visa from the Thai Embassy Washing DC while I was in Indonesia.
I am not sure I fully understand your question but I will share my experience and maybe you'll find it useful.
My most recent experience. I applied for a non-o marriage visa while I was in Thailand. I went to Indonesia, I then received the marriage visa, I then returned to Thailand on that visa. Hence, you can apply now but it wont be "activated" until you enter Thailand (which means you must first leave Thailand). Bali is a great place to do a border bounce and it's not really that more expensive then going to a neighboring country.
I have had good luck with the Thai Embassy USA being very flexible with issue visas while not being in the USA. That process takes a couple of weeks. I don't know where you're nationality but perhaps your home country's Thai Embassy are equally flexible.
From the Thai Embassy in US, it takes 2 weeks (10 business days). I imagine it would be longer during the holidays. I imagine the same is true for whichever embassy you applied.
Your options are probably, wait until you get the visa or cross without it.
In the past I have used bus tickets out of Thailand within 60 days. It's been a few years but the last time I did it, I purchased tickets from Hat Yai to Penang ($12/USD).
There is an Irish lady that seems to run the floor at the local home decor shop, so it's possible. My neighbor is a German national and married to a Filippina so I know he is not here on a marriage visa, he has been here longer than me (8 years), and he has held various engineering jobs, engineering supervisor, etc.
I think another factor to consider is who is doing the hiring and what argument they make, that you are necessary.