I’d go with backpack every time, the roads/pavements are not always flat and so you’ll be damaging your luggage with every knock, even if you get a good one. Plus there’s a lot of stepping on and off curbs if you’re moving around and that’s more hassle than a decent backpack.

Bali probably has the most of the kind of people you describe, then Phuket, then Bangkok, but Phuket and Bangkok you can avoid it easier as there’s more long termers there. Bug spray and stuff you can get on arrival. Got to go walking in the heat to get acclimated and eventually the sweating will drop off but it can take a while. If you can use a fan Vs AC and you’ll get used to it quicker.

Are you discussing a roller speargun? if so, no. Locals get really angry if you shoot fish. They can do it, but you can’t. That’s not the law, that’s just what happens. Expect to get hassled.

If you mean a roller luggage, that’s totally fine… but I recommend getting one that’s a little more heavy duty. Osprey makes good ones. I think they also make one that has backpack straps zipper up. Don’t go to Walmart and purchase rolling luggage that has tiny little cheap wheels. Get something that will last you a long time. It’s an investment.

As far as tourists go, that totally depends on where you are in the city. Phuket is fairly large and the “tourists who get drunk and want to fuck” generally congregate on the one “red light district” street. In BKK it’s spread out in the pockets around town. Don’t expect to get off the airplane and see drunk tourists everywhere you look driving through town. There aren’t that many of them, but they usually hang out in the same areas.