Are you sure all of these steps are actually necessary?
They aren't necessary to get a tiny, unprofitable amount of trade from Aden. You could put a lot of light ships in every trade node (and colonize S-Africa, that one is mandatory) and send a merchant in Aden to steer. But you only have a limited amount of light ships you can use (fleet force limit) and if you don't conquer on the way, those light ships may still cost more maintainance than they give you extra profit. So using this strategy you can only have a few light ships per trade node between Aden&Iberia.
Without the territorial expansion in the Gulf of Aden, you won't draw much trade southwards. If you use most light ships here, then you could get a decent trade flow maybe, but then you'd go to the next problem: the trade node of Zanzibar. You'd have only a tiny amount of trade power here so all trade you have just diverted from Aden will be sucked up by Swahili! And then you still have Congo and the Ivory Coast to go which will also suck up your trade money.
When your trade route isn't that long yet, 50% trade power in Ivory Coast may be very good (easily gained with a few light ships, possibly only 1 conquest). This is because that trade node produces local trade money too, which gets moved towards you. But when the trade route gets longer and more profitable, you don't want to have only 50% trade power when maybe 10 trade value flows in, because then you'd lose a potential 5 trade income per month in only one intermediary trade node... So if you go for a trade route around Africa, the longer the route gets, the more important it becomes to get a bigger trade share. And this is only gained effectively by conquering those coasts and local centers of trade.