So I have never done a wedding cake, and especially not one for 250 people, and I have my first due for May 8th. I've seen the wedding cake cutting guide on wilton, but should I go by that since a most people cut bigger slices? Will a 4 tier, 2 layer per tier be enough once they take the top? Thanks in advance!!

The 1 X 2 X height is the standard wedding serving. Every caterer I've ever seen cuts to that dimension.

As far as servings, check the Wilton.com site and you'll find how many servings each size provides.

Also, when you deliver your cake, be sure to take a copy of your license and insurance. Many venues are requiring proof that you're licensed and inured before accept food from outside the venue.