I like to buy a Lavablade gun on Manhattan at the start, makes those depots go down much faster, can usually get 4-5 before the police come in.
The middle depot at Manhattan contains Polymers, which are worth $420 on Norfolk Shipyard only one tradelane away. The Starflier can pick up 20, total value $8400 if you run from the police (just hit cruise) and sell on Norfolk. That's more than enough to buy a Rhino right away, and you can afford 50-60 light arms for the first trip to Montezuma. One more round trip on Manhattan-Detroit-Montezuma and you can pop over to Mactan for the Dromedary and have enough for 100+ cardamine from there as well.
If you want BIG bucks (not just enough for a class-10 ship), then take Luxury Consumer Goods from Manhattan to New Tokyo and get on the famous diamond-niobium run.