Or is there any chance of something more? You know, just say whenever you need some cash, let me know, kinda thing,
If you REALLY want to know how much he cares about you (as opposed to your bank balance), why don't you ask him
a)if you can have a relationship where money is not a factor i.e. you do not give him any money
or
b) ask him outright how much he wants and, most importantly, get him to justify the amount to you.

He's brand new to Pattaya though (which is probably why I like him so much -- hasn't been hardened by the bars yet), and I've been told I'm the only customer he's ever had.
I met a 19 year old in Bangkok who told me he had only just started working in the bar ( all the bar boys seem to say 3 months, for some reason) but it was obvious that he was VERY, VERY experienced and had been around the traps a lot longer than that. Although he may be new in Pattaya, where was he before that??

he won't even leave me alone when I'm trying to sleep, as he keeps molesting me
That in itself may be a good start. I wish you luck here. But I must admit that a number of guys have been insatiable in bed but they sure didn't love ME. It was something else they were after! 3000 baht a night is a lot and he now might see that as the benchmark and you may have trouble climbing down from that amount. If he puts up any argument when you tell him 3000 is unsustainable, you'll know where you stand with him.

have no idea how to evolve a one-night stand with a go-go boy into something more long-term.
That's where the money discussion has to take place. I also have no idea. If you find out, let me know! Keep a cool head in all of this.
All the best.