If Grizzleheim is too hard at level 20, just go back to your other quests until you level up some more. That's the nice thing about Grizzleheim - you can do it whenever.
Do it when you get to be a higher level. Grizzleheim is not a requirement. You could do it even if you were a Master! It also takes a lot of time, so good luck
Keep in mind that different sections of GH are designed to be completed at different wizarding levels-hence GH being a side quest world, providing break from main quest and little bit of XP and items to use as you progress-so if the tasks have become to hard return later.
:D.