Using your ATM card probably won't be a problem. I can access my account here in Thailand via my Visa debit card through Bangkok Bank. For each withdrawal I make, I get charged the same rate I'd be charged if I were doing that somewhere in the US (about $1.50 US). Of course, Thai Baht comes out of the machine, not dollars.

You'll definitely be able to open your own savings account after you get your visa and work permit. Here in Thailand one needs a work permit to set up a savings account. Individuals who don't work here can't open such an account. However, in more-modern Taiwan, this may not apply. You may be able to open an account there without even being in the workforce.

Your financial situation is pittance compared to another problem you may run into.

If you signed a contract and haven't even been to the school yet, get ready for a potential letdown.
Liars are common in this business. For this very reason, you should always visit your school first before signing a contract. I learned this the hard way after a short excursion to South Korea. My 'institute' turned out to be a simple, run-of-the-mill hogwan. My 'younger high school kids' turned out to be younger high school kids for one class with five classes of spoiled, uncontrollable, rich tykes no more than about 8 or 9 years old. After about five days of that shit, I pulled my always-useful disappearing act.

Good luck. I hope it works out. I hope you don't have to play Houdini like I did in South Korea.