Waiting 6-12 months (depending on the lender) to refinance out more can be a good idea on your first 4 properties if you have the flexibility to wait, but after 4 mortgages, you cannot do cash-out refi (at least not with FannieMae mortgages) UNLESS you do this Delayed Financing Exception within 6 months of purchase close.

Ask the seller if he has more properties or knows of anyone else who may be interested in selling.I am also curious about flexibility, such as pre-payment, assumable (no due on sale), balloon, etc.

When it comes to negotiating, the more motivated the seller the more flexible they are and open to working with you.

The painting business is going great and I have the flexibility to be able to better manage and grow my rental business.I just wish I had started sooner!

Flexible moving terms8.

They have the most flexibility to make loans that dont fit into a particular box.

I was able to run flexible duct in a small attic space in one of my duplexes to get forced air heat and central air installed. 

A lease will tie me into terms and leave me with less flexibility. 

We were also very flexible in that only one bedroom has a queen size bed the other all twin beds, so if one of the guys has an overnight guest he can just go use that room and lock the door and the rest of us will know to crash in another room. 

But having that 30 year vs a 15 year gives you much more flexibility for when circumstances change.