Usually if u want to try having betta with mild tankmates u would add the other tankmates first and later add the betta so the betta doesnt see it as an invasion of his territory... it may or may not work out in your case
Heres my 10 gallon tank with one Betta, 5 harleys, 1 neon tetra, and one nerite snail. Betta is hiding in the anubias right now. The brown items on the bottom are Indian Almond leaves to add tannins.
The tank is on a end table to which I added two more legs for support...works out great and even has storage with doors below the tank. You can see my repurposed wine glass to support a rock with anubias for a Betta rest.