I guess his first "tourist visa" was a visa-exempt entry. He doesn't have a clue. He can do another one, no problem. However, the two land-border entries he already made visa-exempt, could raise the eyebrwos of an Immigration official at the border
20.000.- Thai Baht, not 10.000.- THB. Per Person. The quote on Thai Embassy websites is not correct, Thai Immigration wants to see 20.000 THB or euqivalent in another currency
If you plan to stay in Thailand for 28 days, I presume you have a return ticket for day number 28
This means you check-in at your origin airport hassle free, as you have a proof for the airline that you are leaving Thailand within the period you will get stamped in,
and you will enter Thailand visa exempt and get stamped in for a 60-days stay permit