Hearthpwn

Hi, im a f2p player and began in later Nov. With the G&G expansion i have no time to save money for naxx earlier. Along eht months i earned gold to make the first 4 wings of Naxx and all BRM ( wanted to try dragon decks) 

If i dont have neither a grat base of cards ( even some basic i dont have) I play mostly mage , Paladin and priest and want advice if i should this month get more packs ( needed a second aldor pecekeeper, 2 shadow cabal priest, a second auchenai, i even dont have a second muster for battle, a second minibot o a single spidertank)

i wanted to know if Kel'Thuzad Echoing Ooze o Shade of Naxxramas are more necesary than the ones i lack.

i apreciate advise

As a rule of thumb, if you hesitate between getting expansion wing and packs, I'd say go for a wing. It's a guaranteed value, even more if your collection is filled up, when buying packs means mostly just dust gathering. 

Especially 5th wing of Naxx is a safe bet to invest your money. KT, Ooze and Shade may not be top tier cards as in previous Naxx wings (namely Loatheb and Belcher), but a lot of opportunities opens with those 3 cards, for different types of decks which Pert02 mentioned (I would add Oil Rogue where Shade is a worthy replacement for Earthen Ring Farseerer in 3 drop slot). 

TL;DR

Go for Naxx

Edit: On a second thought, if you are really, really struggling to collect one consistent and playable deck then go for packs. Your fun and satisfaction with playing a favourite and stable deck may be more important than safe and prospective option of choosing guaranteed cards for decks you are not currently playing. 

For the decks you wanna play, i think is better go for packs than for the last wing of Naxx. But if u are gonna pay for it real money, is more cheap buy the wing. GL and HF