Looking at the pictures again I think the short fins are a combination of the pictures and having short fins. They are longer and bigger than the pictures make them look. The tail fin is kind of short but the bottom fin is pretty long. They are all fuller than a lot of the pictures make them look. The beta comes up to the front of the tank and follows me any time I am near the tank. It was nearly impossible to get good pictures of the side of the fish because when I would move to the other side of the tank to get a side shot he would follow and face me. Looking at pictures of other fish online, while he doesn't have huge fins like some, I think he is normal. The fins are also kind of laying down in the pics as he is swimming towards me tried several times to move and take a side pic quick).
I have a lot of spare plants but they are all plastic (many are large but I have a few small ones). Some seem fairly smooth and harmless while others are rather sharp. If plants are good enough cover though, I basically have unlimited wisteria (the kind already in there) to use. I added a pic to the link I already gave of the wisteria (the frog is a dwarf frog and the fish are guppies as far as scale). My other fish seem to love hanging around in it. I didn't think of using a cup but I may have some suitable ones.
As far as the filter, mine is a toms brand (came in a 1 gal tank kit). They are available separately.
I'm not completely certain that is the same size as mine but it looks like it and is the same brand. I read on another forum from someone that tested one out (it was the same as mine) and they claimed it worked fine in a 3 gal but it was a little weak to keep a 5 gal clean. The spray bar is removable so rigging a tube to it wouldn't pose much risk of breakage if I have a suitable diameter tube.
I think toms just took a cheap available filter and slapped their name on it. These are all over ebay for less money and there are at least 2 different sizes (I think). The ones on ebay look like mine in every regard (enough that I think they came out of the same factory).
here is one with the spray bar cheap but it is not US voltage (not sure where this forum is based).
I know I have seen these with US voltage but seem to be having a hard time finding any right now (there are 10,000 filter listings so it can be easy to miss things sometimes). Here is one that include a free adapter to your countrys outlet though.
I am only linking to these specific sellers for reference, I do not know if they are good ones. Also be aware I have seen different sizes of these or similar ones on ebay so look around to find what best suits your needs. Be cautious about what the shipping charges are and what feedback they have when dealing with ebay sellers that ship direct from China etc.
I hadn't thought that the plant would eliminate water changes but figured it and the filter could reduce them. 2 cups would be about a 12% water change (measuring cups) so what about 4 cups (about a 25% water change) more frequently? If its still a bad idea just say so. I just want to minimize any thing that will shock him till he is healthier (like rapid change to different water chemistry, even if only slightly different).
I may be ordering the api master test kit tomorrow (have to see how big my pay check is). Whenever I do get it, can water changes frequency and amount be determined in part by water chemistry ( I would never do no water changes)?