I'm set to close on my first property on the 20th.  

Here are some good places to start: http://www.biggerpockets.com/meet- find and connect with other BP members that are in your area.http://www.biggerpockets.com/alerts - Set up keyword alerts to be notified of the topics that interest you.And, of course thehttp://www.biggerpockets.com/forums - ask any question about real estate!

@Bob Collett There is no set amount.

Find and connect with other BP members that are in your area: http://www.biggerpockets.com/meet Set up keyword alerts to be notified of the topics that interest you: http://www.biggerpockets.com/alerts

The main way I keep track of what is happening locally is to set up keyword alerts.

Have your electrician set this up prior to the 1st day of demo.  

The reason is because closing costs are not(by law) allowed to exceed a certain percentage, and under $35k it automatically does, because most banks closing costs are set.

You could try to isolate the central air value by running multiple sets of comps where the only difference is central air.  

Here are some good places to start: http://www.biggerpockets.com/meet- find and connect with other BP members that are in your area.http://www.biggerpockets.com/alerts - Set up keyword alerts to be notified of the topics that interest you.And, of course thehttp://www.biggerpockets.com/forums - ask any question about real estate!

Some potential drawbacks to keep in mind are:Additional closing and loan origination costs (two transactions/mortgages instead of one) - speak to your lender and title company about costsTwo insurance policies instead of one - probably close to double the insurance cost as compared to a duplex - get a quote from a good insurance agent and compareTwo sets of property taxes instead of oneThese certainly aren't deal killers, and the benefits noted above may outweigh the disadvantages.