I'm a little late to this thread, but I can't help but comment.
I rode into Pebble Beach today (actually yesterday, since it's 2:30am) and they didn't even bother to have us stop. I take it that they do sometimes want you to sign in, but the literature I've seen always says entry is free for bikes, though there is a toll for cars. Sometimes they close Pebble Beach to tourists (usually around big events, like the ProAm), and that may also include bicycles (not sure).
The suggestion to start out at the wharf was a pretty good one. I do a loop around the north/northwest side of the peninsula as part of most of my daily rides. Starting at the wharf puts you on the rec. path, which is a pretty nice bike path, but it will likely be crowded with joggers and other cyclists and loiterers if you're planning on visiting during a weekend. The path does end in P.G. and you'll make a right and ride along the ocean for a few miles to the northwest tip of the peninsula, and then it will turn southwest. Eventually, this road (which will be sunset, by this point) turns inland (and up hill a bit) and you'll make a right, if you want to take 17-mile drive through Pebble Beach.
The weather does not really change drastically here (in fact, its pretty much the same, all year ... cool and damp), but layers is certainly a good idea as the wind coming off the ocean can make it pretty cold, but get a hill or some houses between you and the ocean and it can suddenly feel a lot warmer. It's rare for our temperatures to deviate outside our usual 55-70 degrees.
The rec. path takes you right past the aquarium, if that's something you're interested in. My personal suggestion is that you skip it unless you're going to devote a good half-day to walking through it, it's not very good as a "quick" attraction. And if you're only here for a couple days or so, you might want to skip it altogether.
If you time your ride to end in Carmel, you have a pretty good selection of upscale restaurants to choose from. My personal suggestion is Anton and Michel, which is in the Court of Fountains, around Ocean and Seventh. I believe they have a website, which Google should be able to help you locate.
As for bike rental shops ... I don't rent here, so I don't know who rents what or what their rates are like, but I do know that there are several rental shops. The "North County" map linked from this page (it's a PDF) shows the location of rental shops (yellow) as well as bike stores (blue). I suggest you call the ones in P.G. and Monterey (and maybe the ones in Marina, Seaside and Carmel, if you don't mind driving a bit) to check prices and equipment.
http://www.tamcmonterey.org/prog_bike/bike_map.html