@HotRocks is very knowledgeable in fish disease treatment. IMO the must haves are copper and Prazi. Those are the basics and a good foundation to build on. Meds can be overwhelming when starting out. You will still have losses due to infections but it's not something that will wipe out your tank population like ich, velvet, uronema, or worms/flukes. Once you are comfortable with the copper and Prazi treatments then start exploring antibiotics for further success.Per the mentoring of Hotrocks, I also use General Cure and Seachem focus mixed with food for 14 days (t0 cover internal parasites and worms) as part of my prophylactic treatment along with copper power for 30 days and two rounds of Prazi. You should consider it.
Also, a benefit of Live Aquaria is the 14 day guarantee. If the fish dies in that 14 day period they will credit you the cost of the fish. If an infection is present it will most likely be known within that period of time. That has been my experience anyway.