Many years ago, I kept, bred, raised and sold the Siamese Fighting fish, Betta splendens, as well as a few of their closer relatives. It was a fun and interesting activity.
Calin, the size of your garden looks appropriate for one of the Betta's. There are many myths about these fish that circulate.
First of all, they do not, as a rule, fight other fish. Two males in the same tank or that can see each other will "flare" and fight for dominance. They do not kill each other, although the loser may die later after some time (many days, perhaps months) due to loss of territory, feeding priorities and deportment. That is unusual. Usually the loser will avoid the victor for a few days, then choose to fight again. For entertainment with a single male, just provide a mirror from time to time.
Second, they do not require air pumps or filters, as long as you maintain water quality by not overfeeding and using periodic water changes. They do need more space than the small containers they are sold and shipped in. They need warm water, 76-78 degrees F for best health. An unheated bowl in a 70 degree room will cause loss of health over time. Soft water is best.
Third, they make good pets. They learn to recognize people in the room near them. They will easily learn to take food from your finger tips. I used to feed mine with a tiny piece of chicken on the tip of the finger. They would come to the surface and take the chicken. Occasionally they would miss the chicken bite the skin of my finger. Not to worry, they do not hurt nor can they break the skin.
In the modern world, there are now many different species of Betta's available. Since I was keeping B. splendens, additional species have been discovered, and now international shipping of species unknown then are now easily available worldwide from breeders and collectors. I still keep a couple of small tanks going. I have a casual collection of different kinds of small snails, some shrimp, guppies and a mated pair of Flame Honey Gourami's.
BTW, they now make small filters that are suitable for small Betta containers. I don't have any nor do I know product names, but they are available here in stores and mail order.
Also, check out Bamboo shrimp. I have one that is my latest addition and very unusual. None of the pictures I've seen truly display the weirdly formed "hands" of the shrimp. Instead of fingers, it has filaments that form fans to filter the water. Periodically it closes up the filaments to place the contents in its mouth, located near the middle of its under-abdomen. I sit and watch it for hours sometimes.
The best pic for showing the fans I've been able to find so far is here:
http://shop.sweetknowleaquatic...
Here's a pic of the type of Honey Gourami I have:
http://www.tropicalfishkeeping...
I also am growing a number of aquatic plants in the tanks, probably 8 or nine different kinds at this point. Like the species of Bettas, it is now much, much easier to get nice aquatic plants, many species that were not generally available until just a few years ago.
And I get so excited when I can spot that lone one!! 
Now onward to work on the other part of your dream... 
