The weird things with economy, is that after a while, cashflow means so little. You get huge, steady, bonus income from foreign trade bonus, resort bases, and space port fees (civilian ship building).
If desperate for cash, know that as long as the AI has money, they will always give it away if you got something to trade. Tech is worth hundreds of k, unless the target empire has it very nearly complete, in which case it can be cheap. If really desperate, consider trading a mining base, they are worth tons, but it should bring you all their cash (find one which has a lot), maybe a lesser base, and some tech...
On cargo, amt is ok, that is what we got. I figure reserved is cargo destined for production, or cargo which some ship is on its way to collect. The game could use some improvement in this area.