Welcome to Flyer Talk Philoups

What class of travel are you planning? I take it you already have land transport arranged.

Whatever the class of business I do see potential problem getting this so close to departure. If economy, well L booking class is not a very high economy class and thus likely sold out on popular routes. Business and first are easier, but again some routes (like LHR-JNB vv) are likely to be simply unavailable (and will have been for months).

If you can simplify the routing somewhat, a star alliance RTW may work.

Perhaps it is worthwhile for you to decide what bits are must haves, versus would like to have? I think that will help clarify how to do this.