I think the itinerary looks fine; if it were me I'd probably try to tweak some more miles out of N. America (eg SJU-MIA) but that's probably quibbling.

I've been working on a wee spreadsheet to get a handle on our next DONE4 (most likely starting in August or Sept.) and have taken note of some recent chatter about BA's imposition of fuel surcharges and other fees that are not necessarily the same if ticketing through AA and/or avoiding high-fee airports like LHR.

Depending on where you're coming from, and on your other travel plans, it might be cheaper ticketing through AA and originating at FRA or CDG than IST, given (possibly) lower taxes/fees and no need for rather pricey intra-Europe "positioning" flights. If one originated at an intercontinental hub aside from London (eg FRA, CDG, MAD, BRU, HEL) you wouldn't need to use 2 of your 4 Europe segments just getting to an intercontinental gateway, which might be beneficial later.

Based on my scratch itinerary and educated guesses at fuel charges, taxes etc. it looks (for us - YMMV big time) that we'd save around US$400 all in by starting in Paris rather than IST. ("All in" being defined as US-Europe, intra-Europe, RTW ticket, taxes, getting home after.)

No offense to Ulya and the gang, but $400 x 2 buys a couple of decent nights and meals in Paris.