Should I apply for a multi-entry visa if I plan to stay in Thailand for 86 days and visit neighboring countries?

Get a tourist visa 60 days an extend 30 days =90 days no border runs needed

@Lydia **********

if you arrive with a visa-exempt, you get stamped in for 30 days and the airline will most probably require a proof of onward travel out of Thailand within the 30 days you will get stamped in. This will cost you some money. You can extend the 30 days visa exempt entry by 30 more days for 1900.- THB on Immigration. Then you will have to exit Thailand. You can do a "border bounce" which will cost you around 3500 Baht, come back and get again 30 days stamp visa exempt entry. . . . . . . . to make things easy, just apply for the 60 days single entry Tourist Visa in your country, you will need no onward travel proof to show to the airline, you will receive 60 days which you can extend ONCE for 30 more days on Immigration

You should be fine without a visa. Just purchase one of your flights to either vietnam or Laos to be within 30 days of your arrival in Thailand. Then keep proof of this flight with you and you won't have any issues.

Each time you enter Thailand without a visa you'll be stamped in for 30 days and you can apply one time for a 30 day extension. Given the duration of your trip you shouldn't have any issues with navigating entries, exits and extensions to meet you need.

If you plan to be inside Thailand for a straight 86 days get a 60 day tourist visa which you can extend by 30 days locally

I would just get a 90 day or 180 multi entry visa. And yes they are checking much more often than years past.