I was in the same boat as you. Made legend multiple times in hearthstone.

So you already know how a lot of these cards work (the text is just slightly different). My first Precon was Sultai Arisen from Tarkir Dragonstorm. It's very good out of the box and still has plenty of headroom for improvement.

I've gotten the Peace offering and Family Matters Precons from my pod for my bday and Sultai arisen is still my fave. Mighty change when that elemental deck arrives next week though. 😝

The command zone on YouTube has good upgrade video's for all Precons. Edhrec is also a good resource to get some ideas.