you can apply for a Multi Entry Tourist Visa only in your country of residence, using the E-Visa online system of the Thai embassy in your home country. You cannot get it inside Thailand or at the border . . in your case, through the e-visa system of the Royal Thai Embassy Bruxelles
yes, absolutely no problem. The METV has a validity of 6 months starting on the day of issue. Within this validity period, you can do unlimited entries into Thailand ("multiple re-entry permit"). On each entry, you will get stamped in for 60 days. . . . at the moment, there is a little controversy if you can get a last 60-days stay permit when you do a last entry shortly before the visa validity expires, which would mean that you can actually get a stay of 8 months out of the METV. . . some people report that the last entry was rejected, but I assume it was for a different reason, maybe it was something personal . I don't know for sure, you need to check reports in the FB-groups that tell about the multi entry tourist visa
"You would still need to do Visa extension after 60 days" , , ,sorry but this is complete nonsense. There is NOTHING such as a "visa extension" . . . . . . You enter on a METV, you get stamped in for a 60-days stay permit. This stay permit you can either get extended with 30 more days for 1900 Baht on Immigration, OR you have to exit Thailand BEFORE the 60 days stay permit expires (not "after 60 days" because that means you will already be in overstay "after 60 days" !) and on each re-entry during the 6-month visa validity, you get stamped a new 60-days stay permit
what Immigration meant is that you can add 60 days on top of the 90-days stay permit you received upon entering Thailand. You are married to a Thai wife, which means if your marriage is acknowledged and registered inside Thailand, you can apply on Immigration for the "60-days Extension based on Family Visit" for 1900.- Thai Baht on top of those 90 days. You need to show them a freshly printed Kor Ror 22 Thai marriage registry printout from the Amphur and you wife should accompany you
the problem is: on the phone, many people just talk any nonsense they pull out of their noses, without real knowledge. A colleague of mine once got told a WRONG info by a KLM Airline staff member . . . . . . That's why I NEVER rely on any advices given on a phone call. I rely only on answers given by email - because I can print it and take it to the Check-in counter, in case some nutcase has a different opinion
I didn't pay anything for the transfer of my Retirement Extension stamp into my new passport on the Immigration Sisaket. It shows that the rules differ between different Immigrations throughout Thailand. I bet you didn't get a receipt for the 500 Baht, so you probably paid for a round of lunch for the office staff 😇