A settler is not in conflict with a Quecha rush. You will want to start your settler build at either size 5 (straight build) or size 6 (3-pop whip) in any case, and until then, you can build Quechas to your heart's delight, maybe detouring to build a Terrace if:
- you get Pottery early
- it looks like your rushing goals will be easy, and
- you will be whipping the Settler
If you plan to remain at size 5 for a while to worker/settler pump, save yerself the hammers (the Granary is less relevant when you are going to be stuck at a certain size for a while)
Use chops to push out Quechas faster when it's efficient to do so -- the main thing to watch out for is to avoid getting more than a Quecha's worth of overflow from your Quecha chops, since any more that will at best turn into gold (3.17 patch) and at work go down the drain (3.19 patch)... even the gold is a poor deal here. If it looks like that could happen, then go the straight-build route for the settler, as absorbing a chop into it could easily make it a 2-pop whip, which is not what you want IMO.
Again, I feel this is a food city (and it will only get "worse" after Sailing), not a hammer city, and trying to make it a wonder pump is going against its grain.
Plus, it has poor synergy with the UB.
Could you expand on that?
Stonehenge gives +1 culture/turn per city, and Prophet GPP. Your UB is a granary that gives +2 culture/turn, and normally you will already want to chop and/or whip out a granary ASAP in every new city anyway... so the benefit of Stonehenge is less than usual for the Inca. (And the Oracle will give you enough Prophet GPP for a shrine, though of course more slowly than if you took both Stonehenge and the Oracle.)
EDIT: I am usually an absolute Stonehenge *fanatic*, much to my own detriment and at the cost of some embarrassing restarted games, since I'm too chicken to just take the failure cash and run. So when *I* say "Don't build Stonehenge," that really means something.
Edit2: fixed quote