Installing Smart Water Monitor/Valve
That blue water service line could be PEX, but it also could be HDPE. If it's HDPE then it might be CTS (copper tube size) or IPS (iron pipe size). Based on the shade of blue I'm leaning toward HDPE, but it's hard to tell in a photo. Use a small mirror to inspect the full circumference of the pipe -- it may have something printed on it indicating the type. You also can measure its outside diameter and based on that narrow down the possibilities. In my (limited) experience, the blue coating on HDPE tubing is thin. If you scraped a little away and found black plastic beneath then it's HDPE. You could also test opacity with a flashlight: PEX is somewhat translucent but HDPE is very opaque.

Because the PVC adapter makes you uncomfortable you could replace it with brass. If the blue tube is PEX then this is easy an inexpensive: use a barbed fitting with a crimp or clamp ring, or use a push-on fitting ("Sharkbite" or other brand). These are readily available in any home improvement store. If it's HDPE, though, you'll need a different kind of adapter. These are going to be harder to find because they're normally sold through waterworks distributors. Expect to pay about US$30 for one of these. They're likely to sell over the counter to the public, but figuring out the name of your local waterworks distributor may be a challenge. If you got lucky at Home Depot you might find a plumbing associate who'd know a name. Somebody in your municipal water department may also be a good referral source.

In any case, I'd adapt the blue plastic tube to a brass male pipe thread and set a quarter-turn ball valve on top. The PRV would be down stream of the valve. Pressure gauges are a fine idea (I've done the same at my house), and if you want to incorporate these, then insert a tee between the valve and the PRV and another downstream of the PRV. Use tees with a threaded branch so you can screw in the right reducer bushing to work with your pressure gauge (probably 1/4").