It all depends on the kind of RVing you intend to do. You're from California. Is that going to be your main place to go? If so, and if you enjoy state parks, you know that Calif probably has the smallest site sizes than anywhere in the the U.S. Having said that, you're from southern California and the desert parks have bigger sites.
We have full-timed for 16+ years and our first choices are always public parks or boondocking. We enjoy scenic places and campsites with some degree of privacy. We haven't had any problems getting our 40' motorhome into these kinds of places. We use many of the same parks that we did with our 33' 5th wheel. We use national parks, national forests, county and city parks and of course, just finding 'our' perfect spot for boondocking. However, our main RVing is west of the Mississippi although we've been east many times but it takes a little more researching the public parks for size but we still found plenty for us especially the Corp of Engineer parks. So size really shouldn't hold you back from public parks - unless it's solely in California. :)
As for slides, one or two would be very sufficient, especially if you go to public parks with trees. It would be difficult with more slides to open them and still fit between various trees. I would say that one in the living area is the first choice and perhaps one in the bedroom. We specifically ordered ours new with a two-slide model because that's the kind of campground sites we enjoy. It's been plenty of room for us.
You'll hear talk of some private parks starting to enforce the 10-year rule although if the RV is kept in excellent condition, those kinds of parks will sometimes waive the restriction if your RV looks good. It's mainly for 'keeping up appearances' in their park, but those kinds of parks aren't for us. However, if you're concerned with this then you should probably be looking at one about six years old or so. Then you can enjoy it for a while until it reaches that 10-year mark.
Good luck in your search!