Risk management begins by being aware of risks, then using appropriate measures to manage acceptable risks. :)    

Now here are my initial questions:(1) In this area, and generally, what are appropriate percentages for vacancy, capex, and maintenance?

I know with the VA loan its 0 down up to 450, and then 25% of the amount over 450, something  like thisI was also wondering what level of leverage you think is appropriate, I know that is a rather vague question but lets say for instance i was going after a 750k 4 unit building in Chicago and it qualified to have 4% down, should I put more down if I can?

Even after paying a generous rehabilitation cost, it seems like a rock solid deal.

I was wondering what the appropriate amount of interest a cash lender should receive on real estate purchases.

Practice running the numbers and then execute when appropriate.

With no experience in the field maybe you should concider going to college...The information you are seeking certainly a REI forum is not appropriate.

It is a tool like any other, to be used when and how appropriate and with care.So what is this tool used for?

Or an appropriate number based on the size of our state...  

REIN is perhaps more appropriately called RIEN ... as in it will leave rien in your wallet!