Worried new mother of beautiful blue betta

[NewFry]

Three days ago I rescued a beautiful betta from his cup in a petstore, being an uninformed fishlover I bought him a two gallon pitcher, some rocks, and a pirate head to keep him company. When I got home to do some research I discovered how much he really needs a filter/ heater/ larger tank. So I'm expecting a ten gallon with all the fixings Friday evening.

But I also stumbled upon betta diseases and now I'm wondering if he has finrot. He has a healthy appetite, loves blood worms, I'm keeping his pitcher heated with a light bulb right now, turning it on until it gets to 80 F then turning it off. I'm also changing his water 100% every other day until I get him a 10g all cycled.

I'm noticing a small thin patch starting in his tail, and his two most anterior, ventral fins have white tips. His dorsal fin has small, uniform red dots that I thought were a part of his markings. None of his fins have dark red or black edges though. Should I be worried, and if I buy him medication could I use it for prevention if he doesn't need it for a cure?