The FPR is rarely ever an issue, virtually any low fuel pressure will be due to the pump itself. On rare occasions it will caused by a cracked/split rubber hose at the pump and FPR. The injectors also may leak a bit too much when very old or when the vehicle is not driven much etc.
If you bought the entire assembly, do install that, it will give you more peace of mind to have it all done. But usually only the pump and screen pieces need to be changed, and the pump kits come with the hose etc. Don't worry about the varying test results, pumps do weird things when they aren't working properly, they can take a long time to die completely.
Take your time on disconnecting things at the tank, the fuel lines can be very stubborn. Be prepared to be very patient there, go slow and expect it to take a while. Some fuel line disconnect tools work much better than others, I like the plastic kind that engage more than some metal ones. But I own several types, sometimes a different one works better. Put the tool on before pushing the two lines together. The trick is to get the tool pushed in all the way, with the lines pushed together. Then it comes apart easily, if the internal clips are not damaged from prior times. I had my Mercury give me hell, because one of those three metal pieces/arms was bent, and the tool didn't engage it. I'm pointing out that sometimes everything may go as it should, and there's another problem. So go very slow always when disconnecting metal fuel lines.