Payments for daily costs (AOE devices, employees) seem to be taken regularly, so if you spend all your money while your storefronts are closed for the night, it will throw your ledgers off balance and you could go negative.

Abuse the Schedule system... I had 1 schedule for doing jacksh*t (do nothing) so no one gets paid unless I need them...

Yes, they basically a freeloader, but at least you didn't pay them you hard earned greens.

Buying stuff isn't calculated into your budget. If you buy lots of furniture or expand then it won't show up in the budget.