It can be challenging returning from a long break. I have played since GvG, but took a break after Ungoro. By the time I came back a year later I was too far behind in cards to play standard and even wild I struggled to compete due to powercreep.
I ended up making a new account, and because of the apprentice ranks I was able to build up a collection capable of climbing to diamond every season for the rewards. With arena as my only gold investment and saving what I dont use I've been able to purchase the mini sets with gold and open between 80-100 packs per expansion at launch.
I cant build a good deck for every class, but I can build most of the top decks for my ladder climb.
Due to the core cards, early part of the rewards track and apprentice ranks it was pretty easy to make one tier 1 or 2 deck to climb in my first season. Grinding to legend is great and all, but the difference in end of season rewards between D5 and Legend are pretty negligible, I find arena a better use of my time unless I'm really enjoying a deck.
If you don't mind spending a little money, I found buying the rewards track a big boost my first season to get my gold, arena tickets and the 2 free legendaries. After that first expansion I could manage without spending any additional money.