Way to use it to your advantage. 

should i be taking advantage of nsp etc ?

They will be much more likely to want to take advantage of you if they know you came in to a bunch of money.

Let's add another 6K a month from current 4 properties between increased rents (cash flow and principal pay down) and I'm looking at 15K a month between cash flow and principal pay down (I consider PPD a form of tax advantaged savings). 

Are there particular lenders that are more advantageous than others?

One advantage to having a separate bank account for each property is that your bank does this for you automatically.

Be sure that you highlight that "selling your house can be easier than you think" with the advantages of working directly with you instead of the more traditional route.

I would use the low rent rates of that area to take advantage of the fact that you can probably make money on your BAH?

Having a realtor represent you or having your license even on a new build is definitely advantageous for a number of reasons I do see some BRRRR properties out there as well.

Another advantage to a heloc is only paying interest on what you use.