You do want at least 10% in my opinion for the renter to have enough skin in the game not to walk away.

Many people will lend 100% of reno costs if you've got skin into the acquisition.  

Wholesaling is a great strategy to master because you have very little skin in the game.  

We have a good one but I get nervous that he'll be irritated with the random questions I send him whenever I see an interesting deal.

Almost all lenders I know, including myself, would not lend to a 1st time investor with no skin in the game.

Typically with investment properties you'll be paying anywhere from 15-25% for the down payment (depending on bank/program) because you're not intending to occupy the property as a primary residence so the bank wants you to have more skin in the game (less risk for them).

This is a special use property which requires larger down payment and the bank doing the construction financing will want to see you with skin in the game, even after the refinance to permanent financing.You can get around this by refinancing with a different bank for the permanent financing.  

The problem with borrowing for your down payment, even if it is from family and not even listed on the deed is that you haven't shown the bank that you have any skin in the game.

It really depends on how comfortable you are with the operator and their plan - because if you do this type of investing in an asset where the cash flow does not cover the interest payment, you are counting on appreciation rather than cash flow and I never want to count on appreciation.This strategy can effectively create money from nothing - you borrow to invest in an asset, pay the loan and interest back and you either have cash or the asset and you have no skin in the game. 

This will help ensure that everyone has skin in the game and is dedicated to making the venture a success.