immigration officers definitely have the mandate to check if you are following the conditions of the visa. It doesn’t happen often at entry, but certainly can. (does happen at extension)
Jakarta embassy is usually fast, was 3 days for me but that’s over a year ago before they moved to E-visa.
But ive seen reports here of less than a week. Though they seem to have gotten a bit more strict on the paperwork. But that’s not necessarily a bad thing
You certainly need an active ongoing treatment while your in Thailand. And actually attending it. Thats the whole point. The medical one is not one to try and cheat with
Sure, then tell them you intend to travel within 3 months. Doesn't matter when you actually travel. The validity is still 5 years regardless. They wont cancel you visa if you don't enter once its issued.
Its very common to apply early with refundable tickets. You can without issue travel later. I didn't even provide (or asked for) tickets when I applied DTV.