Monterey's water temps are in the 46-55F range, but a good part is the year it is 46F. You'll find yourself *wishing* for the colder water, as it is usually accompanied by better visibility.
Diving wet in Monterey? You will be cold. If not in the water, on the boat ride on the way back. Whether you can do it is largely a question of how tolerant you are to cold, but most people who do it for any length of time, or who try to do more than two dives a day, end up with a drysuit.
At what depth though. Most of my dives have been above 60ft and I've logged 52F for nearly all of them.
This sunday I did two dives, one off a boat at Mola Mtn., max. depth of 85', and the other at the Breakwater, hitting 49' at the metridium fields. Lowest temp on my computer was 46 deg. in both cases. My buddy on the first dive had 48 when I was showing 46. While there's usually an upwelling in late March or mid-April, this one's been hanging on for awhile. In any case, it's usually sometime in June before it starts warming up significantly.
As to wet v. dry, right after I got certified I did up to 4 dives a day in a 7mm Farmer John and Jacket. But I was swimming a lot and the weather was cooperative, just as it was on Sunday. Later on I changed to a 7/5mm 1-piece with a 6/3mm hooded vest, which was a more flexible combination, but I shivered a lot in either outfit during the SI. I wouldn't dream of trying 4 dives a day when it's cloudy/foggy, windy, and cold, which is much of the year in Monterey. As others have mentioned, you'll freeze during your SI diving wet with any wind, especially if you're boat diving.
I remember one rainy day we were boat diving in Carmel bay, all of us but one were in drysuits. We were all cold on the trip back, but the poor guy who was diving wet was mildly hypothermic by the time we got back to Breakwater (ca. 45 minute run), despite being wrapped in a hooded dive jacket with his girlfriend hugging him the whole way (note, this was in RIBs, not commercial dive boats with more wind shelter). Even with a drysuit there'll be days when you're shivering after a boat dive, but you'll recover a lot faster. When I was diving wet I used to take a thermos of hot spiced cider with me for the weekend, and I needed it; I haven't needed it diving dry.
I use 5mm gloves after making do with 3mm initially. Whatever extra dexterity the 3mm might give is nullified when you can't feel your fingers 30 minutes into the dive. Many people diving dry also use dry gloves. As to hoods I consider 6-7mm the minimum, if you're going to dive wet then I'd seriously suggest you get one of Otter Bay's 12mm hoods, most of the people diving dry around here use them too. As to wet boots, 6.5-7mm. By the time the OP has re-equipped himself with all that neoprene he's probably more than covered the cost of a good used drysuit (I paid $340 for my CF200X, a steal) and an undergarment, and you'll be a whole lot happier and getting more dives, especially first night and early 2nd morning dives (if you're anything like me).
So, for 2+ dives a day, and/or 2 or more days a trip, go dry. It'll be worth it.