RVing in Federal and State Parks
1.Although most Fed Parks do not have power/water hookups, is the same true for State parks?
There are many US parks that do have water/electric connections and a few that have sewer. Most Corp of Eng. have them, some Natl. Parks, and several agencies. Many Natl. Monuments have them. As to states, it depends upon the state. Most state parks do have at least some hook-ups and a few have full. For states check the website under parks and it almost always will tell you. Many county parks also have hook-ups. I suspect that at least half of the public park campgrounds have at least water/electric.
2.Most parks have size restrictions. How strictly are these "maximum" length rules enforced? Do they give you a foot or two?
As fulltimers for three years and RVers for 30 years, we have never been checked for length. But the restrictions can be for several reasons. Often it is due to the length of the sites, since as was stated, most were built when RVs were smaller. But some are due to the roads into the campground. We have seen roads that have turns that are too short for longer RVs and we have also seen dips that the longer RVs can not cross. And we have seen RVs that were hung up on a dip once and on a tree in a turn twice, as well as one that had dropped a wheel off of the edge of the road in a turn, all due to ignoring the length restrictions. So if there is one, check it out before you enter with the RV.
3.Although possibly to broad to answer, what type of "pad" are you likely to find in Fed/State-concrete, asphalt,crushed rock, unprepared,etc.?
I have seen all of those in parks. Some core parks will have paved pads and some states as well. Others have gravel or some other natural material. And we have seen some with just a bare hillside. Again, the internet can help you to determine what is in each park.
Hope that this is helpfull to you. Happy travels!