Very cute tank!

You very possibly will need to up the light some more even for "regular" plants, but you certainly can give it a try with the lighting you have. Whether or not the plants become etiolated will tell you.

You will likely be wise to install a pc fan or two to run 24/7 in the tank. Doing so will greatly reduce mold/fungi issues and will help keep the front glass from fogging over.

There are a number of mini growers that would do well there. Places like Black Jungle, Glass Box Tropicals (tell Mike that Paul -- his orchid plant buddy -- said "hi"), are a few places that sell useable plants. (Even I do so occasionally when I divide my plants. I'm just a hobbyist not a business so it is a once in a while thing for me.)

Bonsai would not be a great idea. Shrubs/trees would require very good lighting as well as very good air circulation to remain healthy. The former is difficult to accomplish in a terr -- especially one that size -- without overheating the tank. Bigger issue is that bonsai need to be regularly root and branch pruned -- very challenging in a terr. Also said plants would send roots throughout the tank making removal for pruning very difficult as well as getting into any filters you many have (should you decide to do a water feature). Without pruning, they would quickly outgrow your terr. Can't think of any non-tree/shrub that would achieve the same look but stay small off the top of my head. (Be neat if you do find something that would work.)

A small water feature would be possible though you definitely would have to go with a false bottom at that point. Google will help you find useful YouTube and other entries there. IF you should go for a water feature, plan VERY carefully so that you can easily access any motors or filters in the tank. You will cuss yourself out in the future if you don't.

There are definitely a number of mini and micro mini orchids that would do fine there though you first will need to determine what the temperature range in the tank will be. Also, with orchids better lighting is likely and air circulation is a must.