i have not been a part of one this large but done several deals with lots of vacancies and repair issues and it can take much more than you anticipate to make it happen.

Anticipate they will counter (as a perfunctory act) of doing their job, and then you can counter back with your best shot!

Learning to really value properties supported by what the market is doing is a good lesson that can prepare you to anticipate possible down times.  

The project will take longer and cost more than you anticipate.  

also return on investment is one thing but return on time is another -sounds like a possible low return on time depending on what type of renter and turnover you are anticipating there

I do anticipate probably moving to Evernote as we grow.

Sometimes life happens and a property that you intended to hold as a rental has to be sold sooner than anticipated, but if you can prove you intended to hold it as rental, for example, you could still qualify.

Anticipate having PM issues until you find the right fit.

Finally add in what you anticipate labor to be.

I'm learning quickly you need to adjust the percentages in the calculators when you're looking at the dollar amount it will create when anticipating different rental rates.