You are correct - F2P is Free to Play.
Blizz allows us to play as F2P at lvl 20. U can play as a starter account at 20, or if u let ur sub lapse u can still play all ur toons at 20. A sub that has lapsed is also referred to as Vet, and a Vet can play at 20 with or without sub.
You won’t have to profession swap like a F2P since u r sub’d. I shared the previous link more for what enchants / gems u can use and places to get gear.
Twinking is all about getting the best gear / gems / enchants for ur toon. To gear a twink to the absolute best gear is probably just as hard as end game, possibly harder. But it’s a cool challenge.
Just wish we had PvP in a better place.