Chicago recommendations and overall approach?

I’ve been doing some research on rings (girlfriend is adamant about a lab diamond and who am I to protest?) and saw a lot of online retailers that are recommended, as well as people that have gone the route of stone online and having it set locally. I had a few questions I was hoping to get some help with if anyone has the time. Overall looking for a 3+ carat cushion or asscher cut of high quality (4c).

1. Does anyone have any Chicago recommendations for stone, setting, or both?
2. What are the cons of the setting being bought online? Is it more sizing and quality control? Having someone local if there is an issue? Something else?
3. Is there any consensus on “top” sites for stones or complete rings? I’ve seen Ritani, Plum Diamonds, Rare Carat, etc. but would appreciate any knowledge and experience here.

Thanks!