I always check before leaving the counter, but in my case, one of the "perks" 😂 from being from a country that cannot enter visa free, is that they'd never stamp a 60-day stamp on my passport.
You don't sound like a "real tourist", so you better convince them (not me, I have no say on this) that you're a tourist, if you want to enter as one. If they don't believe you're a tourist, even having a METV won't guarantee your entry into the kingdom next time.
Korea has its own digital arrival card AND electronic travel authorization called K-ETA, but most people don't need it. It's nationality based. And if it's a connecting flight, you don't need it either.
Thailand DTAC is mandatory for everybody (non Thai passport holders), for each entry.
No, not yet approved, and very likely it'll be rejected as you're supposed to do the first always offline. Either way, they'll send you another email later saying whether it was rejected or approved. If approved, then you don't need to do anything else.