if i started playing do i only need witch queen?

[frog]

or do i need to buy the other 2 as well

[Mez Koo]

Each expansion is its own content as well as each season. You can enjoy Witch Queen as a whole experience on its own with its replayable campaign with multiple difficulties, its patrol location filled with secrets, the 2 variations of the wellspring activity, a raid if you're into that, and its various side/post story activities such as the investigations board, altars of reflection, lost sectors, exotic quests, and crafting/leveling the weapons. Season of the Risen is its own story line that branches off from Witch Queen.

[Mez Koo]

As far as if you want the legacy collection you can read about what is in the 3 dlc that it includes in my guide: https://steamcommunity.com/sharedfiles/filedetails/?id=2787897465
You can also just play the free to play content before buying anything: https://steamcommunity.com/sharedfiles/filedetails/?id=2691498745

[Fubous]

If you haven't yet, try out the f2p for a while to see if you like the grind. Witch Queen Deluxe is probs the best value if you're gonna sink some time into the game, you get the current expansion and a year of content. The other legacy dlc is nice to have, cool exotic weaponry and content to play, but you don't need it for the current stuff.