foedan

I'm not sure how you got this idea, but I can assure you that purchasing the dlc is not mandatory, and that it is not part of the main quest of the game.

I'm playing on hard. Some parts are a good difficulty, some I find too easy. But also, two optional bossfights (flemeth and high dragon) I've had to temporarily skip, to come back to later. These fights are way harder than anything else I've faced so far in the game. On my next playthrough, I'll probably try nightmare difficulty, switching back to hard when things get too tough.