I am making a 12" 10" 8" and 6" with 3 extra 12" cakes...is this enough for a wedding with 250 invited but 190 rsvp'd? I'm using wiltons serving sizes which I heard are off? Would this be enough or too much?

I'm going to be making them 3 layers I think

Each 12x4" Round cake tier serves 56. Making them 3 layers tall won't change that because they will be cut into 1x2x6" servings instead of the usual 1x2x4. Just gives them more cake per serving rather than give you more servings.
The 10x4 serves 38; the 8x4 = 24 and 12 servings from the 6x4.
So you should have a total of just under 300 servings. I suggest just 2 extra 12"ers OR 3/10"ers instead. Let the customer make the call as to how many servings to end up with.

Thanks! Do most people do 3 layers? I just wanted it to not look squatty.