I'm about to buy minecraft on the mojang site, does any dlc come with it or do i have to buy it?

There are no paid DLC for minecraft. All future updates are completely free

Once you buy minecraft, you're good forever. No membership fees, no paid dlc's, the intitial pay is the only time you have to pay anything

There are no official DLC fro Minecraft at this time.

There are mods/ Many, many, many mod. But those are unofficial. They are also free, but they must be found and downloaded separately.