You can have some lucky bamboo in the water (but have the leaves above water). Lucky bamboo won't need much light & will suck out some nitrates. you might be able to do some really low light plants like Java ferns .... but being that the light is not directly over the tank, only a fraction of the 28W will get to the tank. It is prob. too little to do real aquatic plants. (Or house plants for that matter.)
Although a betta can live without a filter, it is generally better to have one. They also do better in a setup that is larger than a betta cube (I say 3-4 gal
min). And a heater is a good thing to have as well.
80 gal FW with 30 gal DIY wet/dry/sump.
9 fancy golds, 1 hillstream loaches, 1 rubber-lip pleco (C. thomasi), 3 SAEs, small school of white cloud minnows, planted.