I am in full support of corruption if it makes my life easier....but even have to watch that these days. Better to follow the rules and cover the bases.
20k in cash is written in the conditions for a tourist visa. So they can ask any time. If they ever do and you you have no cash it would not be fun to go out again. People tell stories that they have been in many times with no problems. If they are ever asked to show 20k one time, they should tell that story to the immigration official.
And also, if you will travel a few times in and out, re-entry available at the airport before you leave as well I believe?? 5am - Midnight...or am I wrong on that one??
Yes for sure. If the comments help and it can be done without an agent then all good. I avoid agents whenever I can. As you said yourself in your comments, Korat is known for problems. I hope he can get it without the agent. If not, then it is agent time.