If you have other partners and don't want to affect the ownership percentages draft a note stating he terms and conditions of the loan to the LLC.  

I understand that, as a buy-and-hold investor, it is important to set aside a certain amount of cash in order to cover maintenance and capital expenditures.It seems a bit odd, though, that these are typically expressed as a percentage of the gross monthly income.

In a lot of leases, holdover tenancy will result in additional rent, sometimes at an increased percentage.

@Tom PortThe down-payment percentage can vary.

As to where you should be searching for Multiplexes, I have provided you with a map (see below) of all of Dallas County and the percentage of properties that have 5 to 9 units for various sub-markets.

In your opinion, is an acceptable percentage of ground lease rent of the total gross revenue?

The lists I have purchased are for targeted areas with absentee owners and another list with high equity percentages. 

For signing on the loan, you can give him a percentage of the deal or an upfront fee at closing.

Why would anyone assume that by simply retaining a set percentage of the rent can/will cover it. 

In multiunits you can count the other units as income to help qualify for the loan but only a certain percentage of the income.