Well there ya go. Looks fine, but I'd still be concerned as to how BA would react at LHR on the way to the Kingdom. I'd allow extra time so that they can (if possible) issue you a boarding pass for the return. (It will be on a different PNR as it's your first OWE segment, so might not be completely straightforward.) I would absolutely have something printed with a Saudi Arab government emblem on it somewhere describing what that web page shows.

I once did a LHR-MCT-LHR turnaround and the BA people at LHR couldn't give me the return BP in advance (because MCT-LHR was using an AA code.) So I had to get it from the (non-BA) service counter at MCT in the middle of the night. I couldn't go landside at MCT due to a bunch of Israeli visa stamps in my passport (and was so advised by the Omani transfer desk person) so had to wait around until the plane was about to board. I certainly wouldn't have wanted that to happen in RUH - no beer in the lounge.

If you're going to make EXP as it is, then no worries. Fly where you want to go. But remember no Plat/EXP bonuses on JL segments.

I have had serious problems with changes to BA tickets and would second the idea of currying favor with the AA RTW desk. That said, while AA does the issuance on behalf of RJ for ex-AMM tickets when using the online tool, I'm not sure that those xONExs carry AA's (01) ticket numbers, so the RTW desk might balk. You might phone them to see how it would work. In any case I'd probably try to have at least one of your transoceanic flights carry the AA code, even if it's on CX or BA metal. That would probably grease the skids with AA if you want to use them to sort out changes. Note BA (and QF, don't know about CX) charge "administrative" fees for date/flight changes even when they don't require a re-issue.