I came into SGN airport 2 days ago at 10 am. Big warning, the immigration queues took 1 and a half hours to clear, there was massive queues and heaps of people. Also if you need visa you can buy it online and it cost $25 usd for it. This is the correct site, I used it myself and all good.
I have dual sim phone. I only use sim cards and not esim. A sim card with Dtac is cheaper in price for me. I get 50 gb of data at high speed for only 300 baht for 30 days.
My passport is full of Thai Tourist Visas (the sticker ones). Sometimes they miss it. Sometimes they just ask, you have visa. 2 days ago I just told the immigration officer that I had a visa and she checked it and stamped me in. My wife was given the 30 day stamp instead of 60 days and she was told by immigration to go back to original place of entry to rectify it.
In Thailand it must be registered. No one in their right mind wouldn't do it. Putting the law aside, what about accidents? No registration means no insurance, are you up for paying huge hospital bills for both the other person and yourself? Just register and insure it.
Suvarnabhumi airport at the Basement level there is Superrich and Happy Rich exchange booths that offer good exchange rates. If you are going to Pattaya then TT Currency Exchange or Damini in soi Post Office. The photo shows the airport ones.