This weekend it rolled off just south of $510.

Review all leases and match them with the rent roll and ledger.

I've been looking at buying RV Parks, Boat Marines and or Mobilome parks, I've read that SBA and HUD do have loan programs in these areas.My question is who do I contact to help get the ball rolling and pre-qualification. 

I would get the ball rolling with your new PM, onboarding, photos, etc so that once Jan 18th hits they can flip the switch and turn your property live.  

Old school ledgers and rent rolls written on notebook paper...

With this being my first apartment deal I am more unsure about underwriting this type of deal and was hoping to get somebody who is more experience in multifamily to look at the proforma, T12 profit and loss, and rent roll to tell me if I'm missing something or to let me know of things that I should be looking out for.

My only backup plan if I can't get verified funds is to assume the worst and to drop my counter offer even lower than my original due to the risk I would be taking on, and then when I do my in person inspection try and guess what rents are fair market for the empty units, and ask as many tenants as I can what they pay in rents monthly.Seller should give you all of his bank statements for the time he owned it, plus the operating financial documents (including rent rolls)that he received when he bought.Then find an apartment broker in the area and find out about rents in the building and in the immediate area.

Quote from @Billy Smith: Having all or most of your rentals paid off is a great feeling with the cash flow rolling in .You know have a bigger shovel to buy more properties , folks get the fever want more more dam the debt full speed ahead .I read a lot saying what  is the rate of the  note ,you could deploy the money in  ,gold ,stocks etc....With just a couple rentals paid off in A -B area I put my kids though Division 1 state college.  

Once you start doing deals, you can roll the profits back in to the business and start doing direct mail - I’d start with your D4$ list and then add other niche lists as your budget grows.

Your living expenses get rolled into the investment, which can offset the expense (you're paying $1300 in rent each month--including that in your calculations for either a duplex or a home with an adu may make the investment numbers work better)I would strongly encourage you to spend a lot of time figuring out how to make a house hack work for you guys.