Looking to purchase TSW Geneva rims 19x9 ET:30 with P265 40R19 tires. Going to go with a squared setup, will I require any spacers for the front wheels?
I run 9.5" rims with 275/40 tires, square. ET is 35, and that puts the rear tire about flush with the fender side. I run a 5mm spacer in front "just because", i.e. makes the front close to flush with fender, and provides a bit more clearance behind the center cap.
Note my wheels are not TSW Geneva. But in general, as the rim gets wider, you want the ET to increase by half that amount. For example, going from your 9" ET30 to my 9.5" ET35, we would expect ET to increase by 1/2(.5") = 6mm.
So I would say you will be fine, and have plenty of suspension and fender clearance.
If you want to go wider, you can run my setup of 9.5" with 275/40 (or 285/30 undersize diameter) with no issues. Personally, I consider 10" to be the maximum front width and then the clearances are pretty tight in the front and the offset must be exact. 9.5" width offers the most in tire choices, because both 275 and 285 are viable choices for that rim.
[Edit: I forgot to mention that the wheel's spoke design can occasionally be an issue. The non-PP GT Premium car has the widest calipers, which can interfere with some spoke patterns. In that case, the spacer is a must to regain clearance.]