which studs should i get?
what 3mm spacer should i buy?
Do you really need studs for 3mm spacers? If you do, you absolutely must buy open-ended lugnuts. I had 5mm spacers with studs, and even my longer-style lugnuts bottomed out before they were able to fully engage the wheel.
I've had good luck with Ichiba Spacers/Studs and H&R Spacers. If you use hubcentric rings, there might not be enough hub left protruding for the ring to sit correctly, since most are tapered 'wider'.
should i run spacers in the back too even though they will clear?
I wouldn't. When I ran the spacers on the Baja, I just used 5mm's up front and nothing in the back. 3mm per side is a track increase of only 6mm.
how much difficulty am i going to have fitting 235/40/17 with 3mm spacers in the front on my wagon?
should i plan on getting camber plates now so that i will have less difficulty?
Are you worried about tire-Strut contact or tire-fender contact? Because camber plates do not change the relationship between tire and strut (your hub is bolted to the bottom of the strut).
Though if you DID want to buy camber plates, I could help you out for a discount on the rear brakes.