You inspired me to try a WC (my first ever) with GB myself! Although I was playing on Normal, I'm happy to report it was successful.
However, roundabouts 1500 I noticed I was losing a ton of tax revenue from Golden Horde and Middle Eastern provinces due to the distant overseas modifier and not having enough ships for max tariffs, and not having a land bridge between my Western Euro provinces and everywhere else, so I just capital moved to Thrace. You're in Europe, but you have a land bridge to Asia, so you don't take penalties on any provinces! That helped hugely with my money situation.
Edit: I guess BootonFace already pointed this out. However, capital move to Balkans (I chose Thrace because it made me feel like a Byzantine emperor) can solve without having to conquer a bunch of high-BB European provinces!