I won't say that I've enjoyed every bit of it, but I think I've done pretty well without buying anything. It makes the full decks/boosters seem a lot more like something to be anticipated and savored, that's for sure.
With the changes to ELO, you could probably get by with just buying 50 credits and then aiming to get above 1200 each week getting you 10 credits. being able to buy and sell on the market makes a big difference too
do not buy the 120 credits as they cost the most per credit (this should be looked into); you would be better off buying 2 x 50