Wow, lot's of questions. So where to start? The routing. Your itinerary is fine and valid. However, it is not optimized in any way. Which means it doesn't make use of the possibilities a AONEx offers. It all depends on how much time you have available.

If you want to optimize, add some segments in North America and maybe a long flight to the middle east in Europe. You can get a nice flight on BA F to DOH, MCT etc. for free.

Weather it is worth adding a continent for a flight to CCS is up to you. The business class is nothing to write home about but still nicer than economy of course.

In terms of redemption value, most people here prefer AA because of the low taxes and you only need very few miles for awards. You will even be able to get status with them via the Platinum Challenge if you have enough segments on AA. Be aware that AAdvantage doesn't earn miles etc. on US TATL segments so you need to go to LHR with AA not BA if you credit to AA.