I’ve been there so I’ll share some of my perspective.
1. sounds like your tank is not cycled which can be a big problem. I too were eager to put fish in new tanks and had my sufferings. I’m personally not against a fish-in cycle as long as you know what you are doing, i.e. jump start with some BB product, feed light and up the water change, and most importantly monitor your water parameters.
2. PBs are hard to keep when they are young in my experience. I’ve had them die from bloat, ich, banging into the glass, jumping out, starving for not taking non-live food etc, that I almost gave up.I eventually decided to buy multiples in the beginning, treat with ich medication at first sight of ich, mix pellets with bloodworms, etc, that I finally get to grow 3 Orinocos to 8 inches currently from fingerlings.
so good luck and enjoy the hobby.