Hi Dan!
Gena and I were diving at North Park about 6 weeks ago. Here's what I remember. North Park is located at the north end of the dam. Enter the park from FM 306. Be prepared to pay a few dollars per person at the park entrance. Be prepared to file paperwork with the gatekeeper to include license plate, your name, your home address, city, st, zip, DL #. The gatekeeper will claim that he doesn't want your information but then will immediately demand it and plead ignorance. "It's not my policy. It's just policy"; but he can't tell you why it's policy.
He will also try to tell you that you can dive for free on the south end of the dam in proximity to the project office. Don't believe him. That is a hike followed by a mountain goat trail followed by a mountain goat entry. Pay your money and stick with North Park.
As I remember, the water level was approximately average. North Park entry location was reasonably simple but not trivial. Water temperature was in the 70s as reported. Visibility was approx. 6 - 15 ft. somewhat variable. All in all, I would call it a typical lake dive. Be warned, the boaters were crazy and did not respect the dive flag. When we were there, there was also a sail boat (quiet - no motor) regalia competition in the area. The sail boaters, at least, seemed to try to be respectful of other people.
Air fills and dive shop? No clue.