I've never used QuickBooks, but after investigating, it seemed that I would have to go with the Desktop version (versus the cloud based version). 

If you're just renting out individual rooms in your primary residence, that wouldn’t typically fall under ADU laws. --- So, if you're renting out rooms and everyone shares common spaces like the kitchen and living room, you're in the clear of those ADU rules.

This method provides several advantages against a traditional manager as I can cater my service and fees to the individual needs of my owners. 

I will not know the downpayment % expectation or your individual peculiarity,  for when you're ready.

Wrote letter to random individual How did you finance this deal?

Even without a track record these individuals presumably know you as an upstanding and trustworthy guy and this means you only have to sell them on the merits of the real estate.

Can someone please advise me on the pro's and con's and keeping the lot as a single lot with all 14 duplexes on it or subdividing each lot to have 14 individual lots? 

My spouse and I prefer not having to split things up and retitle ownership under separate individual trusts.

Is there a faster method then sending applications to individual tenants in response to their request to see the property?

I will say that the borrower has a better chance to negotiate on the fees, interest and when they are to be paid with a private individual lender as opposed to a hard money style lender (that has more overhead).