What is my biggest risk buying 3 properties

[Orlando Goodon]

I'm new at this. I've done a spreadsheets to break down numbers. I'm searching loop.net, grabbing the listed gross income, maintenance and tax figures. Then go to mortgage calculator and calculate mortgage with fees. Net incomes (minus mortgage)average  $2000-$3000/month. I plan to pay off these mortgages in 6 years by dumping all the money back into houses+$1000. Will take $3000-$4000/month to reach my goal. Keep in mind will be putting aside money each month for maintenance.

If I plan to hold these properties as long as possible, what is my biggest risk? They would only be slightly under value due to light work needed like paint, so a housing crash would hurt fast (Only $30k down on each). However why should I care? I'm not after appreciation. I'm after equity and net worth and soon, rental income without mortgage, so $5000/month.

Only think I can think of is:

-Housing crash and each property looses up to $20k in value (so what? No flip)
-Recession and tenants leave and rents go down ( I loose $200 per unit so $1400/month less so now I have to pay about $800 ($1800 total now to stay on target) more per month (Fine unless my income goes down by more than $30,000/year)
-All 3 have roof/plumbing issues at same time (should not matter; each house has a separate maintenance budget to cover this)
-All three need work that far exceeds the maintenance budget (Would need loan perhaps, but this is highly unlikely to have an extreme situation with all 3...BUT....it COULD happen)

Would LOVE your thoughts! I've even heard people saying paying mortgage fast is not good? Why would that be? You build equity fast to resist depreciation and skyrocket your profits fast...AND OWN 3 properties in less than 10 years AND livable INDEPENDENT/PASSIVE wages well before retirement age!

Seems too easy! :)