Full hookup has a fairly consistent meaning: the site has its own water tap, its own sewer inlet and its own electric pedestal, so a guest never has to move the rig to dump tanks. Water and electric only is usually called partial, and those guests use a shared dump station on the way out. Dry or primitive means no utilities at the site. Some listings stretch "full hookup" to include cable or wifi, which is marketing, so ask for a site map with utilities marked.
The amp thing is real. A 40 foot fifth wheel running two air conditioners in July wants 50 amp service, and a park with only 8 of those is quoting a narrower slice of the traveling market. Pull-through means the rig drives in one end and out the other without unhitching, which big-rig drivers will pay a premium for. Back-ins are cheaper to build and rent for less.
Where I'd push harder than the site count is capacity in the ground. Ask what the electrical service to the property is, in amps at the meter, and ask for the septic permit showing design flow. Going from 30 to 50 amp isn't a swap at the pedestal, it's new wire and often a new transformer from the utility. Adding sites needs septic capacity you may not have. New site development commonly runs into the tens of thousands per site once you count sitework and utility runs, so a park with headroom already permitted is worth real money over one that's maxed out.
