I'm up to over 1m cash now, it's just rolling in. Managed to optimize my resource buildings, and finally moved my colony to a new island for more space, so I'm now on about 16,000 income and 11,000 spent, meaning 5000 profit
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I gave up with building a Sultan's Mosque, as I just don't have enough space to get the required envoys. I thought it'd be about 3000 Envoys, but you need over 5000, I think.
Make sure to keep the AI as allies, at least at the start of the game. There's nothing worse than someone killing your trade ships and stealing the resources off them. If you have a large trade ship carrying 75 of each building material, you've lost about 10K if that dies, and that's 10K of materials that goes to an enemy.
Note that after I got to about 100K cash, I quit selling anything, all my money comes in from my noblemen and envoys now. I'm now making a "military island", from where I'll then set about killing everyone else. Only one of them has any defenses, and they only have walls and a couple of towers, so it should be a cakewalk. I need to kill them anyway, because they're lagging up my map, due to a bug. There are only about 30 houses on their island, but there are literally thousands of people all stuck in the marketplace, and everytime I even go near her island, it lags to hell.
Oh, and make sure to let in any beggars. They are the ONLY way to get more envoys if you can't build any more houses. If you build alms houses, the beggars don't cost you anything, and the extra citizens/patricians/noblemen really help. Although I've turned them down a couple of times, and I've never seen them come back as bandits, like the game says they will.