Just incase you don't already know.
If you're numbers are even close you'll know your there when you see the really HUGE ball floating on the surface at the site. You can tie off directly to the ball if someone isn't there already. drop down the chain attached to the ball and take a course heading of 165 degrees for no more than 50-75 feet. You'll swim right into the bow of the Sheridan. Vis latley sucks at around 20-25 feet, but you can still see pretty good.
All the following depends on how good a captain you are, but IMO a 24 foot boat is more than enough. I've had my 21' dual console out there with 5 divers onboard in 2 foot seas. The only thing I worry about this time of year is thunder storms rolling in. You will most likely not be alone out there as the site is popular, and you're well within VHF range of shore (this assumes you have a quality VHF radio) if for some reason you do have the place all to you're self.
I just edited my Sheridan pics from the last trip out there. In a day or so check out my website for the pics of the site, and you'll get an idea of the vis you're in for.
Have fun.
Dave.