Are you planning to do it through the StarAlliance planning tool? When I used it to plan my upcoming RTW, I found really flaky in respect of keeping track on the validity of the itinerary and even booking certain ( valid) flights. I’ve heard others say the same thing; flakier than the OneWorld version for sure.
Might be gratuitous advice, sorry if so, but could I suggest you look at using a good travel agent? They are good at finding code shares for a given flight which will attract lower carrier charges and many other things to improve an itinerary. Plus, in this day and age of cancelled flights and schedule changes, they will have the responsibility to keep tabs on those and find alternatives, rather you standing in some airport, trying to call some airline call centre trying to figure out a change.
I give my TA the itinerary that I have planned and figured out and then ask, “can you improve on this?”
There will be a charge, small in comparison to the overall cost of the ticket and ss I mentioned, you get the ongoing backup if you need it.