Once you start putting money in the banks, the need for any other money making venture becomes irrelevant. But with caravans, take a look at short hauls along safe routes - Cherkassk/Azaq-kale to Moscow, Moscow - Smolensk, etc. Spend some effort to work out what sells consistently well, on which route, then go for it.
Provide your own guard by riding shotgun on the caravan, by patrolling around it, till you work out the safe routes, but then don't scrimp on caravan guards.