For example, lets say I find a lender and they say yes I will fund your down payment.

I realize the extra cashflow, and I can always make additional principal payments.  

. $4500 seems like A LOT of money to transfer our digital plans into CAD (the contractor already built-out our design ideas on his laptop's software) and have an engineer ensure we're using the right beams in the right places.

You sound like you have a similar background to where I was coming from - my folks had me mowing grass and fixing things, collecting rents and making payments for their rentals business when I was younger. 

So with just $100K, you could put a down payment on three or four properties and keep a good chunk for reserves, let tenants pay down your mortgages and either keep the cash flow as supplemental income or devote it all to rapid pay down.

Inspection cost-Lender fees-Closing cost-Mortgage payments-Property taxes-Utilities-Insurance-Commissions-Selling closing cost-Home warranty-Termite letter-MLS fees-

And what kind of payment agreement to have with these guys?

I was able to pull those down payments out off thin air basically.

I realize this is a super basic question and more info might be needed, but I wanted to see what you all thought: Do I pull out the cash from the refinance to continue to fixing up the property or do I use the cash to put a down payment on another unit?

What percentage of  tenant income do you figure  is needed  to best  insure monthly payments ?