I'd only use a heater in the winter if the temperature in your house goes below 70F, I keep my frogs at 70F personally, no heater.. I really am reluctant to use a heater because these frogs are not too bright and will burn themselves on it very easily unless you manage to put some kind of protection around it. Not sure if that is worth it on a small tank, better to just keep the ambient temp. at 68F-72F.

A filter is needed, get a tetra whisper that is double the size of your tank (so if you get a 10g, get a Whisper 20i).

If you want substrate I would recommend sand.. do not get jagged sand though like Tahitian Moon. I use pool filter sand in one of my tanks and I personally use CaribSea's Moonlight sand in my frog tank.. I like it cause it's the finest grain sand they sell for aquaria (it's not good at holding down plants though).

I wouldn't get toys or flowers or anything. I actually keep a lot of plants in my frog tank, anubias, vals, pennywort (floating), wisteria, and a few others. I think more than anything they really enjoy the floating plants cause they will rest in them at night with their noses poking out of the water. If you get a lot of plants you'll need some decent lighting though of course.