I've been raking in the gold and I'm currently sitting on over 5200 gold. I've come back to hearthstone around a month ago and I only have a few cards. I opened 60 packs of classic, Frozen throne, Old Gods, and Descent of Dragons.
Is there an expansion to go into or should I wait for Scholomance to come out and get 52 extra packs for that?
First of all - only you can really answer this question for what works for you.
That said - We are in the third and final leg of this year, so for this year it makes the least difference in terms of which expansion you buy cards from (2020-wise). However, it appears (on face value) that Scholomance is shaping up to be a very powerful set, and not only that, many cards also seem to be dual class. So for your 52 packs, you may get the most playability out of this set.
But ultimately, what you may want to do is look at some decks (either older ones or ones for this new expansion) and find a deck you like the look of. Then use your gold for packs that give you the best chance of getting the cards to build that deck.