The beauty of Eheim filters (and many other canisters, actually) is that flow can be metered to suit your needs. I used a 2213 on my Ebi that housed shrimp at times and tiny fish at others. Absolutely no issues. Definitely not overkill. A 2211 could also suit your needs but there's no room for growth and you really couldn't use it on a larger tank if you decided, say, to get a 12gal tank in the future. Use of a spray bar is a good idea if you don't go the lily pipe route.
If you select an HOB, go with an AC 20. Or, really, an AC30, because the tank is rather tall for such a small volume of water. You could cheaply have a piece of glass cut (complete with rounded front corners) to serve as a new top if you do that.
If you get a heater, definitely get one that allows you to adjust the temperature. There are infinity brands from which to select. Just don't skimp on that front and get a temperature controller no matter what you do.