They are social creatures, so you would definitely want more than one. You could add 3 frogs and not be overstocked, however I don't recommend mixing ADF's and fish. A couple issues can come up: First being the frogs are nearly blind and can have a hard time competing for food with the fish. And second there is the potential for frog on fish or fish on frog violence. Many a frog has ripped up a betta and vice versa. This is not to say some aren't kept together successfully long term, but it's risky. It's also possible adult frogs may hunt those embers. They may be too small to mix with the frogs IMO.
Whether keeping them alone or in a community, it's best to feed them in the same spot every day, so they know where to find their food when they smell it. You can use their fav hidey hole or cave, or even use a feeding dish. In a community setting I would place the food somewhere discrete where hopefully they can get to it before the betta. I would hand feed them when feeding frozen foods since any betta will surely sniff out worms or shrimp before the frogs get to them. Only feed the frogs thawed frozen foods and frog and tadpole bites(HBH brand is great). I alternate every other day between the two. They have sensitive digestive systems so avoid any other types of pellets and freeze dried foods. Much like bettas, they do best at 80 degrees, and with care taken to assure there are no sharp eges or pokeys on plants and decor that could damage their sensitive skin. They loove live plants...especially ones that allow them to rest at the suface, such as pennywort. They often dash up for air and dive back down quickly, slamming into things in the tank. Be sure everything is firmly planted in the substrate and cannot be knocked over by a frog so they can't become pinned and drown. And, of course, they need a tank with a good lid.