I can't remember, one of them has a higher limit. I have a Thai bank account now so hasn't been an issue for me for a while so I've forgotten which it is. If I find the info I'll post
What Wylie said, especially if your own bank doesn't charge extra for currency conversions. All banks charge a flat fee of around 200 baht for a withdrawal of any size and and most allow a max withdrawal of
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baht but one allows more than that so have a Google and that will be the best value for you, should you need that amount of cash
Looks like you're from UK so go for your 60 day tourist e-visa, however, as you state you want to visit surrounding countries then you could just come in visa exempt and just do each visit before your 30 days is up. If, for whatever reason, you decide you want to stay in Thailand past 30 days at some point, you can go to immigration and get a 30 day exstension there
you can get two years out of it by exiting the country before the end of the first year and then re-entering with another 12 months health insurance. At the end of the second year you will have to depart and do a brand new o-a application