Don't use a water softener, unless it's RO they will not do good for the fishes long term. Water softeners exchange calcium and magnesium for sodium or potassium. While it makes the water 'softer' it also makes it much more skewed in parameters as it raises TDS, conductivity and I believe general hardness. It's really bad for fishes and seen many loose fishes eventually due to them. It basically doesn't really make the water softer just removes what makes limescale. RO is great, often needs to be remineralised but that's because it removes everything hence you get waste water rather then an exchange. There is quite the difference so that needs saying. In my opinion for many fishes jumping is largely due to a trigger. I have known jumpers who have never jumped in my setups. It can be water parameters, can be being spooked, can be for food, could be other things. If there is erratic movement around a tank that can trigger a lot. Cold water changes shouldn't be an issue, most fishes are able to deal with them without issues, my barrier is around 5-10c changes depending on the fish. Pythons are expensive in the UK, but hozelock does hoses with many different fittings for the range of taps we have here. If fishes are having an issue I recommend the new water hitting the tank in a way it'll disperse. I do recommend Corydoras for seasonal fishes, fascinating fishes. But they wont go that cold, just unheated inside for most.
Algae is more natural then most plants. Most of those plants are terrestrially growing. Looking at natural habitats of fishes usually there is few plants. Plants definitely don't increase stability or anything. Corydoras are not clean up fishes, neither are Otocinclus and some are extremely specialized even those commonly available.
