Partial hookup means electric and water right at your site.
Yes, you leave your tents and all your stuff set up for your entire stay.
No, theft is not a a widespread problem.
However, do keep valuables locked up in your car, on your person, or at the front desk lockboxes.
Your tents, coolers, chairs, towels hanging out, etc. should not be a problem.
If you bring bicycles, lock them to a tree or lock them at the bike racks at the outpost and settlement areas.
There are many, many threads on tent camping here. Just poke around and do some searches.