I don’t really understand this comment. Perhaps you are using “cycle” to mean something different that I am used to. Your tank has a filter, so the media should be building up bacteria. If you want plants, you will not be using carbon. And mulm should develop in the substrate. By all means, stick with whatever works for you. But I just don’t understand why you would need/want to do 100% water changes weekly.
And, a lot of people with planted tanks do massive water changes. 50% weekly is pretty common - some do more. I have never heard that water changes alone were unusually rough on plants. Just suggesting you might be able to grow far more than java moss despite the size and frequency of your water changes.
twix - bettas really aren’t much work at all. Really comes down to whether you want one larger fish and a couple of other critters, or a school of littler fish. The biggest diff I see is if you want to spend $6 or so for a heater, and don’t mind seeing the heater in your tank.
A very very general rule of thumb you often hear is 1" of fish per gallon. But not every piscine inch imposes an equivalent bioload. And, a planted tank will process a greater amount of waste. And a lot goes to personal taste. Some folks prefer much more “crowded” busy tanks, others prefer a sparse look. Both can be done quite well IMO. But I would suggest smaller tanks do better with smaller bioloads. By nature of their small size, nanos can be more susceptible to changes in conditions than larger tanks. Generally, the larger the tank, the easier it is to keep stable.
My seat of the pants recommendation - if you go with guppies, I’d probably put 3 in a 1 gallon. Or a single betta. Think of whether you want baby guppies or not. If not, get all males. Breeding can be fun and interesting, but you’ll need to have something to do with the babies.
If you go with a 5 gallon, you could obviously include some more - or a couple of different species. You might want to try a small school of tetras, which might exhibit schooling behavior. Neons, cardinals, rummy nose. Or maybe white cloud minnows. Tho they’d all probably prefer a heater.
With a 5 gallon you could have - say - 1 betta, 3-4 guppies, a snail, and a couple of shrimp. The shrimp and snail tend to eat detritus - as such, they don’t tremendously increase the bio-load. If you use a heater you could get a dwarf bristlenose catfish, a couple of algae-eating otocinclus cats, and/or maybe a small school of 3 of the smaller cories.
As I said above, I personally like Endler’s. I’ve noticed that in some LFS they sell “feeder” guppies that very closely resemble Endler’s. A buck or less a piece. Have very colorful bodies, but lack the large fan-shaped tails of fancy male gupps. And lacking the big tail, they move somewhat differently.