Hello again everyone, thanks for all your replies, they've been very helpful.

I managed to find out that - whilst the port in Venice does not indicate any trade income - I can click on the expenses and income list and it says I'm getting 200-300 florins from Venetian trade. So it turns out that I do have quite a widespread and wealthy trade network after all.

My biggest problem is the ships disappearing. I've tried clicking their names on the General List and it switches to a completely empty stretch of sea. There's not even visible enemy ships around in that area, so they're not hidden behind. It's like they only exist in name, they've totally disappeared otherwise.

Oh, and I didn't know spies could do so much, I need to start churning them out, I've also discovered the awesomeness of emissaries and bribing armies! Got Navarre, Provence, Champagne and Flanders through it (I cheat by the way, shame on me ).

It's really annoying how the idiot child is the oldest and inherits the throne before his genius younger brother!

I might move up to normal difficult, I find easy hard enough though, and I've had the game for a few years now!