My main fear is expanding too quickly and if I have a vacancy or something unexpected with one of the properties I don't want to be sitting on multiple mortgages I can't pay.

As long as you have access to a lot of capital to fund renovations, vacancy, and unexpected items, not to mention can handle the stress,  and trust me--t will be a lot, and it's a lot of stuff no one  (except BP!)

You should figure out how much it cost to replace each component of a house in your area using builder grade material and the lifespan of each component.

Keep cash on hand and hide it somewhere safe for all of the unexpected issues coming your way. 

I'm glad you were able to recover some of your losses, but it does remind me that the contract dissolution component is just as important as the daily operations component.

If they are late, talk to them-- maybe they had unexpected medical bills, maybe a funeral, maybe a car accident/problems?   

The product has a builders risk or rehab component built into it. 

Doing a large value-add component where you recoup all/most of your cash to offset cash-on-cash return of minimal cash flow.

While away for a month I shut down the ice maker & it froze the ice cube eject components causing a failure. $100 Repair clinic part & it was fixed. 

In case you are eligible for the Solo 401k, here are some of the benefits it would offer compared to a self-directed IRA:Solo 401k contributions limits are roughly ten times higher than IRA limitsThere is no custodial requirement for the 401kYou don't need the additional expense and administration of an LLC to have checkbook controlThere is a built in-Roth component whereas IRAs are either traditional or Roth, not bothA spouse can also participate in the same Solo 401k planThe Solo 401k has additional tax benefits over an IRA when investing into real estate using leverageThe penalties for prohibited transactions are less severe, though it's best not to utilize this benefit :)