Do not use CPR's holes on the right or you'll have to put a smaller post on the top like I did. They are off enough that the ball can't drain with the bigger normal post in there.
Get an automatic center punch to put a new pilot hole where it belongs. If you have to make the entire hole bigger that's fine, you're drilling through it anyway, and the bottom of the post covers it.
Definitely drill all the way down for posts if you aren't using the carriage bolt style from the original playfield, CPR's wood is harder than the original and you will snap posts.
Double check the maze area before drilling, everything has to be 100% correct up here or the geometry won't work.
Consider the posts behind the 5 bank moving them back a very slight bit (if you can.... still it's part of the maze!) - If you use new 5-4-3-2-1 targets they will tend to brick if not.
Get a larger drill and precut the clearcoat around holes once you've decided where to put them. I make sure I cut it bigger than the screw so there's no possibility of the screw twisting the clearcoat as it cuts its threads. I changed as many of the posts as I could to machine thread type just because I like them better (if you snap a machine threaded post, you can remove the T-nut and pound the post down through the PF since it doesn't thread into the wood at all) If you're using the original carriage bolts make sure when you pound them up through the PF you won't lift the clear using the same clear cutting method. Do NOT use the drill bit in a drill to do this! It will bite in and make a mess of things quickly (which the post should still cover....but still....). You just kind of run it by hand lightly to cut out the clear.
That's the high points that I recall from doing mine 10 or more years ago. Be very careful driving screws and posts into anything where it's near an edge as if that screw snaps, you have a real issue on your hands getting it out without damaging the edge. (Dealing with that on a Joker Poker right now..... ugh.)
I have a drill guide (cheap at hardware store) that I keep around, put the post/screw into it, then select a drill bit that's a size or 2 down (to account for the threads if it's a wood type, use the same size drill if it's a machine post).