Hey, I might recommend having guppies or similar fish, they are shoaling fish and would work very well in your tank. It’s roughly 1 gallon per fish but if you are planning to keep some babies leave room for them to grow x
When I had my fry I put them In a smallish separation tank in my main tank while they were small. This was to easily keep the water fresh without having to change it. Because a lot of mine survived, when they got bigger I moved them into a 10 gallon tank once they got to a size I positively knew...
You shouldn’t worry at all but I understand why your paranoid cause I am to about small things too!
If your tank has a lid they won’t be able to jump and if the tank feels unstable/wobbly then I would change the stand but if not it’s fine xx
If it was parasite then he might have had Anchor worms even tho the holes don’t look that much like them maybe do a little google on it and see if any of the symptoms look familiar!
Sorry I’m not that knowledged on diseases I’m sure someone else will come