Before you go stocking NP I'd do more research into the pros and cons. The problem with stocking a top line predator is that you cannot tell them what fish you want them to eat. If you will continue with the C&R only in the pond, then I'd look into stocking Tiger Muskies instead of NP. They won't spawn and possibly over eat your LMB. Check into the spawning habitat requirements of NP and see if they would spawn in your pond.
Baby steps first, before you do any stocking of different fish species you have to get a good sampling of the Relative Weights of the LMB and BG in the pond. In a pond that size, making a mistake in stocking fish will be a very expensive one to correct.