What are the rules for extending a Multiple Entry Tourist Visa and re-entering Thailand?

Anyone here on a Multiple Entry Tourist Visa? I am in Thailand already and about to finish my first 60-days stay. A couple of points are not exactly clear to me:

1) can I extend each of my my 60-days stays for 30 additional days or I can only do it once?

2) how long do I have to stay out of Thailand for? I understand land borders are closed, but is there a minimum stay?

3) which process shall I follow once we come back in Thailand - since I already have a Thai Pass from our first entry: do I have to ask for a new one? I would just be entering the same details as my first Thai Pass..

4) For those who have some experience already, which country is the best option these days for no or limited quarantine and easily receiving the TP once heading back? Travelling around is not super easy at the moment 🙂

Any info appreciated! Thanks!