I've had (single) bettas in several community tanks over the years, 10-20 gallon. Agree with nearly everything said above: avoid anything with ANY tendancy to get nippy, and avoid anything that itself is a big 'nip me' target. And avoid anything you don't want its eggs/fry eaten, of course
I've not had good luck putting zebra danios with bettas, actually - swordfish either (nipping the bettas fins). I would discourage anyone from keeping Mollies in a community tank as they are such ick magnets and your other fish really don't need typhoid mary as a roommate
(Plus they do better with a bit of salt in the water, not ideal for most other community type fish such as tetras and corys)
If you have corydoras or loaches, PLEASE put in a nice small herd of them, they are NOT really solitary fish. Not only do they seem much happier and grow better when in groups, lone individuals sometimes get nippy. (Yes, even corys) I would suggest at least three.
Kuhli loaches are neat but be aware that they are basically hidey and nocturnal fish. I've had a lot over the years and a number have turned into fairly exhibitionist creatures over time, spending a decent amount of time out in the open during daylight... but some never do, and it can take as much as a couple years before others decide to show themselves on a regular basis. In a reasonably well planted and appointed tank that is. Actually I had one 20 gallon that I put 4 kuhlis into, only ever saw one, figured the other three had died somewhere, and then 4.5 yrs later when taking down the tank for a move, found the other three kuhlis still in there, big and fat and happy. NEVER saw them
This is something to consider in a small tank where you are real limited in the amount of total fish you wanna put in there.
I've not had problems with water current with bettas, but I have never been one for really big whoooooshing filter currents either
For your fish's health it would really be a good idea to let the tank cycle for at least a month EVEN WITH 'OLD' GRAVEL (which is definitely a good thing to add, unless there have been disease e.g. ick problems inthe tank it came from). And then load the tank gradually, over a period of a number of months.
And really, the fewer fish you put in there, the better. A 10 gallon with a betta and maybe 3 modest-sized corys (the pandas are nice, and stay small) and maybe 3-4 of one kind of docile hardy tetra or platies, would be a nice setup, IMO.
Have fun,
Pat