That completely depends on which cards you have in mind. The core set will change and several expansions will rotate out, while others stay. Crafting anything from Descent of Dragons for example would be a waste, unless you also play Wild. If you just came back, you might as well wait till the next exp and craft any cards that will be auto-includes in the new decks.
Rise of Shadows, Descent of Dragons and Saviors of Uldum will be rotating out. Scholomance did great when it comes to how many of the legendaries actually see play. Which classes do you main and which legendaries do you have in mind?
I would wait see how the new meta pans out and from there you can make any choice you like from any expansion and choose your main format at same time. However if you are more set to standard play then definitely just wait, good things come to those who are patient.
I've been playing a few games a month for some time. Also bought Outland exp packs when it came out, didn't like it too much and did not play. But I guess I might come back once new exp hits, so I'll be crafting only then.
That's a good call. A lot of things will change, such as a core set, new mechanics, old legendaries getting changed, various class cards getting buffed and nerfed, set rotation, etc. It's been a while since I've been hyped about HS, but they successfully peaked my interest again after a long time.
I only have been playing mage, shaman, paladin most but I want to play more classes like warlock which scholomance has a lot of legends from there. I just spent all my gold on packs hoping for legends and got nothing :(