If you have the necessary funds, I would just go for a letter from your current employer. It makes it easier for them to just tick that box and move on to the next application.
Self employed would mean more paperwork, more thought, more work. No one wants that.
Off topic comments on threads like those need constant monitoring by admins. If the admins are online at the time then, although it’s a bit time consuming, it can be done by admins deleting off topic comments. If they’re not online (admins have lives, other things to do) then things get out of hand quite quickly.
In some of the groups I admin for, people are quite responsible. In others, not so much.
It is allowed, otherwise you would’ve been refused entry. At every border they can ask you to show cash and, in the case of tourists, onward travel tickets out of Thailand.
No it’s unlikely to be a problem but in my situation for instance, the border is 40 minutes away so it’s cheaper and easier to cross the border than it is to go to immigration.
Always best not to overstay. If you’re near a border, depending on which one it is, it might be cheaper and easier to hop over the border and back into Thailand again.