Welcome to the Forum!
Square is better than staggered.
I have 18x9 +42 wheels and had Prokit springs.
18x9 +42 should fit stock suspension and lowered on Prokit springs, depending on tire width.
But, without some room between the wheel/tire and spring perch, you won't be able to add camber to tuck the top of your front wheels. This is why I started by adding a 10mm front spacer and 5mm rear.
I didn't feel like the wheels were flush, so swapped out the old spacers for 12mm front and 15mm rear. Now my wheels sat nice and flush with just prokit springs (for natural rear camber) and one set of camber bolts for the front. My camber was -1.8 rear and -1.4 front. Drove 65,000 miles with this setup. No weird tire wear.
I know a 225/40 will fit without any other mods. ( no spacers, no camber bolts, no other parts)
I'm running 245/35/18 all around. (this size tire has the same outside diameter as OEM)
A 255/35/18 will fit with spacers. ( this is the biggest size that I would recommend for a 18x9 wheel)
My car is post#5 in this thread.
https://www.ft86club.com/forums/showthread.php?t=132552