Brock Lesnar 265lbs. He wasn't the biggest fighter. A strong guy could pick up a 140lb guy and smash him against concrete. Eddie Hall fought 2 guys at once last week. Smashed them both. He is over 350lbs.
At age 25yo I can see the fun in drinking. At an older age it's not that interesting and gym provides strength and happy hormones as you say. Having a drink with dinner fine but drinking regularly it isn't much fun anymore.
I'd visit every beach on Samui and KPN if I was you. 3 weeks on each island. Apart from HH and CM those 2 islands would interest me. A point of note there are direct flights between Surat Thani and CM so you can travel more cheaply and split time.