You can change money at the airport basement level B. Superich usually give the best rates. You can also get the skytrain from there to the centre of town and it is very cheap. Get the aircon bus to Pattaya from Ekkamai also very cheap. If you want to go straight to Pattaya then the bus counter is on level one. I paid 300 baht last time
Bus from Suvarnabhumi Airport to Pattaya. Takes about 2 hrs with aircon. I paid about 300 baht. All areas are safe in Pattaya. Book somewhere for a couple of nights and then move if it is not for you. Taxi is quicker but costs about 1600 baht but make sure you fix the price before sitting off.
International incoming texts are free on UK sims so I keep a cheap one going. I pay £2.50 ($3.28) a month via PayPal, and I have a 2 sim phone. You can do the same on some later 1 sim phones by using an e-sim.