From what I have read you still need spacer unless you change wheel/rims. As for the warranty from what I have read the warranty is only void if the modifications you do, lift, etc. cause a problem.
My plan is to go with lift/leveling first. Nothing bigger then 2.5" and then look at tires. I want to avoid the domino effect of modifications, lift and tires that leed to new gearing, new wheel etc. for a vehicle that I love but will be doing 95% street driving.
I've got a Rubi on order and have same question you posted about the leveling kit, tires, warranty. Did you ever find the answers? I like the sound of the leveling kit, because I don't want to get too far away from stock and all this is way over my head. Do you know, if you get the Tera flex performance leveling kit, do you have to worry about spacers and all that if you just get a little bigger tire on stock rims?