I have done this run a number of times. IMHO, after leaving the Cape you should head for St. Helena and then for a point north of Recife. Make sure you do get north of the bulge of Brazil otherwise you will find the current taking you southwards.
Once north of the Amazon you can choose your own moment to tur towards the Azores and then to Gib.
I have sailed up and down the west African coast in motor ships and down in in a sailiong vessel. Sailing south you have the favour of the Canaries current which gives you a nice run from the Canaries to Cape Verde. Sailing northwards I would not like to head into the current. Also, you get winds off the Sahara at tmes which even far out to see covers the boat in a fine red sand. Closer inshore it is worse. Sand in your mouth, in your winches, in your clothers, in fact everywhere is not so good. Even if the particles are small they are stil abrasive.
As for pirates; I don't think that is a majour concern in this area but again, it is another reason for doing the "double crossing". By doing the double trip you should also get favourable winds most of the time.
As for the Benguela current, be careful. Once leaving the Cape and after passing Cape Columbine you wil not be close to the coast and, as you pointed out, the current is in your favour but the water is cold and both fog and near gales ar not uncommon. The further out to sea you are the less the chance of fog.
Unless yopu are heading for Luderitz or Walvis Baai, keep wel off the Namibian coast. It is not really trecherous but it does have some surprising tricks to play on you regarding fog, unpredictable currents and a lack of any ahrbour other than those two I have already mentioned.
Enjoy the trip!