I forgot that the MP400 is a QLC drive, so I would probably avoid it. Looking at the TH review on it, it has slower game loading times, than a SATA Crucial MX500. A WD Blue SN550 would be a better pick. I believe you were looking at the P5 plus, which is a gen 4 drive. The non plus is gen 3 and cheaper. I filtered the drives by make, 1tb, and sorted by low to high price. I would say the 970 evo is the best price/performance pick, with the WD Blue SN550 being a more budget oriented choice.
I would just go ahead and clone your current install, to the new drive, as long as you decide to stick with your B450 board. If you decide to upgrade to a higher quality B550 board, you will need to do a fresh install.