And then you can use that information to start to develop your own personal due diligence method: Crowdstreet.com, 1031 Crowdfunding, Akr7, Finresi etc.

Rent was due by 5th but no communication on late payment and is not responding to my text/emails. 

Box solely for the purpose of collecting rent but I do suggest having one and if nothing else works use it for rent collections but I would Electronic payments or bank deposits before doing mail.

What property management software or tools would you recommend for tracking rent payments, leases, and maintenance requests?

Find Brandon's videos on YouTube for the "four square" method of analyzing homes and practice.

I use Buildium for tracking rent, fees, leases, and collecting online payments, but I don't use their reports for much, as I end up copying my online banking each year into spreadsheets.I've been using Rental Hero for the last hour and already impressed with it.

Find Brandon's videos on YouTube for the "four square" method of analyzing homes and practice.

What % of purchase price is smart to put as a down payment? 

I assume you currently have a residential mortgage that does not have a pre-payment penalty.

We will either bring on another investor each year to make the yearly payment or we will just forgo the income payments to the partners and make the yearly house payments out of the cash flow if we just want to keep the property with only 7 investors.