While we are not adding size, we are able to add a bedroom within the existing footprint.  

I've heard things ranging from "15% of gross rent" to "$2 per square foot to maintain in its current condition + $0.50 per square foot to be put in savings for a rainy day fund".Obviously you need to go in more depth when seriously considering a deal... but what is the rule of thumb that YOU tend to follow when estimating maintenance expenses?

Take a 30,000 foot view of the general direction (real estate) and start to whittle it down to 20,000 and 10,000 foot until you finally get to a laser focused niche view of how you want to proceed. 

I found a house on the same block, only 2 houses down that that sold a little over a year ago and the price per square foot was $3 cheaper.  

Are there any CRE professionals out there that could give me some advice on how to get my foot in the door with a firm?

We did have to add a couple large footings for new load bearing post locations, and also did a small addition on the back of the house.  

How does your price per foot compare to your most comparable (especially location and condition) sold? 

If so, every time you step foot on the property for maintenance or inspection you lose that personal asset protection you built with an LLC. 

Higher density = higher utility per foot.

The major reason for the cost overruns in my last house was that there was a foot of snow on the ground and there was quite a bit of exterior work that needed to be done.