Another important question you need to consider is what award tickets are you likely to book? Intra-Africa? Africa to Europe? Africa to Middle East? To Asia? To North America?

I would be looking for the best award chart for whatever that answer is, with any Star Alliance mileage program that has decent earnings for ET fares AND that you can get a credit card for. If you are eligible for cards in the USA then quite a few Star Alliance programs are available on a credit card. Keep in mind cards with multiple transfer partners as well like Amex, Chase Sapphire, Citi Thank You, and Capital One Venture, and then there is also Marriott Bonvoy cards which has loads of transfer partners.

Something else to consider since you have Delta miles built up, you can use them on KQ for many of the same city pairs as ET.

On your original post, point 1) Miles don't "transfer" from one program to another. You earn on any give Star Alliance program and use those miles to "buy" an award ticket on ET according to that program's award chart. ET makes certain amounts of award seats available to other Star Alliance partners, usually they are accessible by any of the partners, so choose the program that is most advantageous for earning on revenue fares, has a credit card in a country that you're eligible to acquire one, and has a good award chart for your desired routes.