Hearthpwn

If your really stuck and already bought your packs and opened them, don't craft anything yet.

Go to hsreplay.net, create an account, download their decktracker or plug-in software.

It will bring your collection to their database. Then you can find out what decks you can craft with what you have so far. Whatever dust you have left from card duplicates can be used to craft a good deck you'll find.

Think you should buy anything that is above collections that are rotating out to wild format this year. ( Buy anything from Ashes of Outland, Scholomance Academy, Madness at the Darkmoon Faire)

If you are a new player, wild format is probably not where you'll want to be now since it is of a larger collection you'll have to collect. Probably stick to standard format for a while.

I have been sort of F2P for a while now. If you spend around 1-2 hours a day on hearthstone, you should be able to accumulate about 8k gold every 4 months which is about 80 hearthstone packs, probably more since the new xp point system or gold earning system is actually giving more than before. That is pretty much enough to get at least 4 legendary cards, all the common cards, and almost all rare cards out of an expansion.

To start with hearthstone and spend no money will be really hard in standard, ranked, and casual. Especially to finish those daily and weekly quests for new players.