So, I got a couple treasure chests with gold and it gave me some cards but I can't figure out. How do you actually equip the cards you get from treasure chests? They don't seem to show up anywhere on the deck management screen.

Yes, they are just unlocked now. So you can get them among the other cards in the scenarios.

 

If you just started playing the game, save gold for expansions and characters before. Expansions are particularly expensive (4.000 each one after the first). If you already know that ignore the last paragraph

Aha thanks. I was beginning to suspect that was the case but the interface and instructions aren't very clear. I already bought the package deal with all the characters and quests so I can just use gold for treasure chests now. I'm going to save up 20k for the big savings deals

One tip for gold, if you're on Android, is to use the Google survey app.  You don't get much per survey, but it only takes a couple weeks to earn the $2 credit you need to buy the daily gold.  By the time that ends you have plenty to buy it again.  I'm on my third or fourth 30 days of gold now.  Lets my buy a chest every day, between winning a couple of scenarios and picking up my 200gp daily.

Yep, treasure cards are all about populating your game with a wider variety of goodies to find. I highly recommend salvaging treasure cards you aren't interested in or have too many of.