Some general suggestions.

Get as many UA miles as you can. With 1 stopover and 2 open jaws being allowed and some quirky routing advantage, it really can do a lot for you if you know how to put it in good use.

Suggest you visit milevalue site for some ideas on how to maximize the UA award and play around on UA site to get an idea what you can achieve.

A good knowledge of the Star Alliance members and their route maps would help a lot in piece a routing together.

You can combine the Asia and the Europe on a single award or the South Africa and Europe on a single award with creative routing.

Alternatively you can investigate the AA's Explorer award that is distance-based. Read the dedicated thread in AA forum you can learn a lot from others itineraries and see how they are pieced together. That can cover both Europe and Asia as well. Though going to South Africa would be too expensive using OneWorld carriers (because you would have to use BA longhaul and as you know that becomes quite a hefty cash outlay due to the YQ).

Use BA Avios for short hauls you bound to need when travel in South Africa, as well as Asia. They come in very handy.

Watch for AMEX 50% bonus transfer to BA - that seems to happen twice or more a year in recent years.

Finally, dont try to cover the whole trip all by award flights. Sometimes it would make things a lot easier if you are willing to do a low cost position flight, or bridge the open jaw with the low cost carriers flights / ferries (between Turkey and Greece in Summer). Your trip would become much more flexible.