My advice is to never ever sit with 300k in your treasury. In my last England game i bought cities from the pope for 30-40k every turn just to sit under 50k. Get above 50k and your generals start getting those bad corruption traits.

I started a new game with Venice last night - playing lategame with "show AI movement" enabled means waiting for 1 minute for each faction to move it's 20 useless diplomats around... Not somthing I'll do again. Venice seems nice, and their starting position is superb. What i did so far:

Take my spy and both stacks over at Milan. Ignore the rebel settlement in Italy for now. On turn 1 i sell map info only to the Milanese for 500 florins. The guy in the village on the Peloponese peninsula goes to take the rebel settlement up north. The guy on the island next to the holy lands just waits and builds the city up. I disband both large navies Venice starts with. Sure 12 or so Galeons are very strong but you don't need them early on, and that gold is better spent on mercs and town development.

Early Italian castles are useless, so all three towns are focused on development.

On turn 2 i reach both Milanese towns with my two stacks, buy the merks and siege them. I sell map info + trade rights to the HRE for 600 gold and move down towards the pope.

Turn 3 - I take both Milanese towns and wipe their faction off the map. The world briethes a sigh of relief as this treacherous scourge of the Catholic world is no more. The Pope was too slow to react so I got away scott free! And since I didn't have trade rights or alliances with them, my rep stayed constant. I now plan to spraed some Catholic love around with my diplomats, getting the Pope on my side, then launching a Crusade at Jerusalem or even Bhagdad. Maybe I'll take Constantinople on the way, sack it and give it to the Pope, to ensure I can launch crusades later vs Byzantium.