If installing a pressure reducing valve, is there any sense in installing a one-way check valve in series, or would it be redundant? (i.e. does the PRV also act as a one-way valve?)
First, no, they don't function as a check valve. They limit inflow by dynamically changing the valve opening so that when less pressure is on the out side, the valve opens up fully, and too much pressure on the out side causes the valve to shut. In a no pressure situation (where water could go backwards), it won't be impeded at all.
Assuming that this is for your residential plumbing, you generally wouldn't install a check valve, because you want to be able to drain the system at the shut-off if you ever need to do any modifications.
Many PRVs also include a backflow bypass, but since this is explicitly described in the product specs, it implies that not all valves include this functionality. And you may be able to find a combination device out there with both capabilities.
Here's an example with a backflow bypass which you can see more details about in the manual.
Without evidence that your device has both capabilities, then all you can assume is that it will prevent a backflow when your inside pressure is below that of the municipality.
I will note that in my experience, I've had the pressure inside exceeded my hot water tank's TPR valve until I installed an expansion tank with only a PVR installed, but it's possible that the municipality has a backflow preventer on their meter. I'm fairly certain my supply pressure doesn't exceed the TPR on it's own (my old valve failed, and the TPR never tripped, but after I fixed my last leaking toilet and faucet, the TPR started to go since there was nowhere left to expand).
Installing a non-return valve (NRV) before a PRV in my experience will produce a very high vibration in the line and may cause incorrect readings if you have a water meter.
I have tried it from 0 distance up to 1 meter; pipe from 1 inch up to 6 inch; all types of valves caused line to vibrate and fail.
Didn't care to get the formula or reason; just stopped doing that.
if you wanna be code compliant use a watts 9-D dual check with atmospheric vent. it will pass inspection for residential, commercial and institutional in every part of the country. you can get one at lowes and depot. If not available there then go to your local Ferguson plumbing supply (theyre the largest plumbing supply in the country and chances are there is one near you.