What tire sizes should I put on 18 x 8 wheels all around? Should I put 225/40/18 in the front and 245/40/18 in the rear?

If you were to use a staggered setup, it should be 225/40/18 and 245/35/18. But since you're using 18x8 all the way, you can use 225/40/18 for all 4 (or even 235/40/18).

Using a staggered setup will look better and have a slightly better grip during launch. On the other hand, you have the advantage of rotating the the tires if all tires are of the same size.