As long as you don’t use Bkk (or Phuket) airports you can probably get by on 6-9 months as a traveller on visa exempts.
But I think anyone over a certain age will not trigger anything by immigration (who’s not intending to stay for long) as they are not really employable material in Thailand.
Depends on how long you intend to stay for on your second trip.
If its under 30 days a visa exempt will suffice. Taking a trip for 2 months then a short break in Cambodia and then coming back to Thailand looks like a normal traveller to me.
The requirements should be all listed there but if they do request a statement like other consulates any printout showing the balance and your name is sufficient.