Hearthpwn

Hello, so back in the day I played Hearthstone quite a bit 4 years ago. Obviously I am missing alot of expansions and cards.  I just recently came back and I am struggling to climb ranked in standard and WIld because of this so I just bought the next expansion Alterac Valley, the Mega bundle and the other one they sell, for a total of 144 packs which I plan to open tonight. 

My problem is there is going to be cards I want to craft old and new to stay competitive and I want to buy more card packs so I was thinking of buying more classic cards since I have most of them anyways. Still missing quite few legs though but If I get repeats I can just dust them and use that as more dust to craft what I want. Is this a viable strategy because I literally have 20 dust lol, or would it be better to buy cards directly from the expansions themselves and hope I get what I want or what? I have enough money to buy 2 49.99 version of any set atm but want to know from you guys if this is smart or is there a better way to go about this? 

Just for the record back in the day I used to dust off a lot of cards that were golden for classes I did not play much or at all so I know thats a thing.

Thank you!

Classic is it's own format now. If you don't plan on playing it or playing wild i'd dust them. You get the free standard core set each year now which includes tons of cards for classes and neutrals. I wouldn't buy any of the pack bundles for the last year's rotation. FITB , UIS and Alterac now will stick around for another year but tbh the cards from these sets aren't impactful as the ones from Scholomance for example. I'd suggest waiting for one of the Pack sales they do ( They sell pack bundles for cheaper plus you get 1-2 legendary cards from each as soon as you buy it ), but if you realllly want to open some packs i'd suggest the expansions of this year since the other ones will stick around just for 4 months. But again if you plan on playing wild the whole thing changes IMO Darkmoon and Scholomance are the stronger expansions from the last year.

I plan on playing Wild and Standard fulltime, so which expansions should I focus on then?