Same as you Snowdog, I tend to getto that stage fairly easy, but once I start building wheat/mills/bakeries, herb/breweries, quartz mines, potash, glassworks my maintenance costs go through the roof. So I build more houses and get back to positive cash flow, but then my population is greater and my basic resources start running out, fish, spices, linen clothes etc. so I need to build more of those, possibly on a new island, maintenance costs go up again and I start losing money, so more houses etc. etc.
I'm gradually getting the hang of it though, even though I keep restarting.