I have Destiny: Legendary Edition (Taken King) code to unlock the expansions and the disc for PS3. I redeemed the expansions code to my PS4 and it said that the expansions are ready for download, but I can't download them. I need to buy the Destiny: Legendary Edition (Taken King) for PS4 or should I buy the Destiny(Standard Edition, without DLC) for PS4 to be able to download the expansions?
The offer to upgrade from PS3 to PS4 (and Xbox 360 to Xbox One) expired a while ago. From the Bungie forums:
The Digital Upgrade program is only for purchasing a digital copy of Destiny for Xbox 360 or PS3, then moving to the appropriate next gen console. However, this offer expired on January 15th, 2015. The only license you can transfer between consoles now is for the Expansion Pass or The Dark Below content if purchased on Xbox 360 or PS3.