Once you've cleared immigration you're "sterile" so to speak so cannot leave the "system" so have to stay in transit in Bangkok. If you want to leave the airport at Bangkok, the first leg of the journey remains domestic so you don't clear immigration until Bangkok. So what has happened in the past to you is correct
says it's too subjective. There's no one company which would suit everyone. Suggest you seek out Robert Jackson who's a broker for all the main companies and discuss your situation and requirements with him
That's nothing to do with a re-entry permit. The 300 baht tax is simply Thai government having a laugh watching the Cheap Charlies go into meltdown 🤣
Unlikely you'll get six months of freedom on an ED visa. These days you have to attend class at least a couple of times a week, and extend every 90 days. You'll get 60+30 off a SETV, and then with a border bounce another 30+30, so you're getting close to your target