I have a few comments from issues mentioned so far.
First, you should have no issue with live plants. Sand substrate is ideal, and the data on the light seems good. My knowledge of LED is next to nothing but this unit seems to check all the necessary boxes. You might have to be careful of the brightness though; forest fish (most of the fish we keep in an aquarium are forest fish) do not appreciate bright overhead light and can pale and be stressed. Floating plants is the easiest way to deal with this (provided the light is not excessively intense) and floating plants also assimilate a lot of nutrients like ammonia/ammonium. Which brings me to thee next issue, cycling.
With live plants and especially floating plants, once they show signs of growth (a few days in the case of floating will tell you) they are taking up ammonia/ammonium and you can begin adding fish. Just go slow. With shoaling fish (fish that must have a group, like all tetras, rasboras, cory catfish, etc) it is always best to add the entire intended group of the species together. They will settle in much faster, avoiding some problems like ich better, and if they are hierarchial this will be sorted out without incident. That deals with cycling.
Bettas are not community fish and they should never be forced into such a situation. Now, it is probably true that some aquarists may have luck doing this, at least for a time [there is more than one thread here where this worked for a time and then literally overnight ended with dead fish], it is risking the fish which no responsible aquarist should ever do. Enough said.
Before we can suggest fish species at all, it will help to know the parameters of your source water. The GH (general or total hardness) is the most important, then the pH. You should be able to get this data from your municipal water authority, check their website. We can go further into this later, but some fish have specific mandatory requirements respecting water hardness so it is wise to know before you start selecting species. Temperature is the other parmameter that is crucial to fish, as the temperature drives their metabolism and they have a very narrow range which varies among species. This we can deal with via an aquarium heater, but all intended fish must share the basically same temperature need.
On the filter...decide on the fish first, then decide on an appropriate filter. In a 40g tank [one of my tanks is this size) a dual sponge filter is more than adequate if you intend peaceful fish like gourami, small shoaling tetras or rasboras, cory catfish, etc. A HOB would be unnecessary and produce far too much water current for such fish. On thee other hand, if you were to decide on a tank of fish like Hillstream Loaches which must have stronger currents, the HOB would be a necessary choice (or some other form of water movement). You also intend live plants, and this reduces the need for filtration to begin with, and many plants do not do well in stronger currents. Again, it is all dependent on the intended fish.
