Buying things in hearthstone

I've never found it worth it to buy packs with gold. I guess it does depend on your ability, but I've always found arena to be a much better payoff.

Honestly it depends on how much time you want to sink into the game vs how much the money means to you. I buy some packs sometimes with real money just because I have the spare cash for it not to make a difference to me, but if you're on a limited budget then it's definitely not worth spending money.

Don't do it. Once you start it's hard to stop. Honestly, Hearthstone is broken and even the pro players admit it, with more and more addons, a newcomer will have to invest around 1000$ to have the cards that will allow to have at least few competitive decks.
I've spent some money on that game and I REALLY regret it. The only thing worth doing in the game is playing arena.