Okay... so I think I found what you need. I pulled this photo from an ad on Sailboatlistings.com and I cropped it into paint with the ruller showing. Then I drew the red, blue and purple lines to mark off the relevant distances you need.
From sailboatdata.com we know the boat is 23.67' LOA and in this photo the boat measures 590 ticks. So each tick is 23.67/590 = 0.04 ft/tick or 0.48 inches per tick.
The distance between the purple lines is 670-240 = 430 ticks which translates into 17.2 feet. So the wheels sit approximately 17.2 feet from the hitch. If your pad ends up 18 feet deep, that would give you a about 9" of play when backing up.
The distance from the rear of the boat to the wheel base is 110 ticks which translates into 4.4'. So if you put some sort of wheel chock across the back of your pad and back all the way until you hit the chock, your boat will be hanging off of the back of the pad by 4.4'. Build some sort of brace off of the back of your pad to address what
@LloydB mentioned about the boat tilting back .... and maybe place a few sand bags over the tongue when parked..... and you should have what you need.
As far as the width of your pad... from this photo
It looks like the sheer overhangs the wheel base so if you go with the beam of the boat and add what you need to walk about the boat, you should be fine. Sailboatdata.com says the beam is 8.33'. If you have the room I'd go with a minimum of 10' for the width of your parking pad.
Hope this helps.
r