I’ve just finished the base game on normal at lvl43 and wondering whether to go to veteran or elite, or buy one or both of the expansions and/or the DLC package. Any recomendations?
If you finished Normal, you can´t play Veteran (it´s only a variant of Normal).
I would buy the two expanions and finish them first. If you still have fun, think about Elite/Ultimate. 
He can play Veteran, but the quests will already be done. 
I wouldn’t recommand to go to Elite now.
43 is quite low, there should be some quests that were missed on the way that can be done in either Normal or Normal Veteran (second option is better 
).
If you can, wait to be at level 50 before starting Elite. This way, when you open a chest, you can hope for a legendary item.
If you don’t want to search for missed quests or to farm levels and reputation, or simply because you want more of the game, you can take Ashes of Malmouth to have the follow-up of the story. It will easily bring you past level 50 in Normal or Normal Veteran.
(I would recommand taking the expansion(s) over simply farming.)
You can take AoM AND Forgotten Gods, but you don’t have to if you don’t want to spend too much.
For me, the second expansion is more optional as it’s kind of a side story and doesn’t bring as much as AoM.
But not optional if you want more Grim Dawn.
(And you can’t play FG if you don’t have AoM.)
Thanks for your help. I’ll do the expansion.