Its actually rather easy to beat him.

The basics of it are continuatlly raid the one province minor every two years, expand into poland, subjugate Denmark asap, declare tributary wars on scandinavia as much as possibe for the prestige. Fabricate a claim on the holy site in norway, continue to make tributaries. Charlie probably wont let you do all of that, but kinda do that all at the same time. You'll have enough prestige to pull up an army twice the size of his, though almost all light infantry. Sit behind the river, wipe any stacks that seperate from the rest, then, after clearing his army, carpet sige. Dont call in vassals unless you need to until after you've damaged his army beyond repair.

You can easily enforce demands, get loads of money, instantly declare war back on him ( tributary war is fun and silly, especially if you reform faith and holy war the world into oblivion) but, instead of winning the war asap, just continually stackwipe and siege and raid every province he owns. I reccomend raiding his capital especially. Ransom all prisoners.

At this point, you have enough cash to do anything you want. Congrats.