I'm having $950 going towards principal every month, along with cash flowing $500/mo.

I have an existing mortgage on the bldg which has $195k remaining on principal; only about $15k remaining from insurance money.

Does anybody alternate between buy and hold, then flip a house to make a large payment towards principal on their buy and holds?

It's correct that you subtract debt service, but you have to remember to add back the principal paydown at the sale. 

Many Thanks  If PP=   $    220,000.00 Purchase Price  $ 220,000.00 Downpayment $50,000 Interest Rate 4% Term 360 Loan Amount  $  170,000.00 LTV 77% Monthly    $ 1,279.72 Principal  $ 472.22 Interest  $ 566.67 Tax  $ 170.00 Insurance  $ 70.83 MIP  $    -   Net Rent After Mortgage    $ 1,436.94 Less Utilities, Trash  $(200.00) Less Advertising  $(50.00) Less PM Fee  $ (271.67) Less Rental Tax  $(385.00) Less Cleaning  $(100.00) Total Rental Fees  $(1,006.67) Net Cash Flow    $   430.28 Less Distribution   $ (43.03) Initial Outlay  $ 50,000.00 Rent Ready 1  $ 10,000.00 2nd Investor  $ (10,000.00) Total Outlay   $  50,000.00 Rate of Return Target 20% 16% Annual ROR Amount  $   10,000.00  $      7,907.00 Over/under    $  (2,093.00)

Nothing else matters.On a side note, you can factor your principal reduction into your ROE and projected appreciation as well.  

Keep in mind, however, if you decide down the road you want to sell one individually you will have to overcome the hurdle of convincing the lender to release that one as collateral....which could mean handing over some or all of your sale proceeds towards principal payment.

Does it make sense to dump some cash into the principal and refi for a lower monthly mortgage to show monthly profit? 

One is principal pay down.

I told him don't you think 90k is a tad rich for a wholesale fee common man.. this lady could use some of that money.. of course as we got in to it ( typical wholesaler that did not know what they were doing) lady owed 210k on it.. and I paid wholesaler 5k  and bought it for 215k.. but I would not have bought I as a matter of principal for 190 with a 90k flip fee..