I have not seen the interiors and some have been vacant a long time, so I am estimating high rehab of $100K or more.   

Second question...did you at least ask them what condition they believed the interior & exterior were in, after they told you what they thought it was worth? 

The whole building measurements include the interior hallways as part of the heated area, but not patios and porches.

They believe unit is in good condition.I need to get interior pictures and would like to start advertising. 

IF yes, what cash offer would you offer as a rule of thumb since I have not seen the interior of the property.... any help and advise is welcome.

Countertops, and other interior items could have a payoff if the area demands higher rents for premium features.  

However; should that not be possible, as to packages for such properties, if you buy an unfurnished property, you may be able to hire an interior designer, to handle the furnishing for you.

I do know if in a historic district you need committee approval for almost everything.If they want exterior and interior preserved to perfection than your projected costs could go much higher.If this project represents a large portion of your resources then it would be a NO for me.

Thank you so much for your input - The house we are looking to purchase is a complete gut we have the money to purchase the home (it is looking good we are going to get it for 15K, it has been vacant for a year and there is some water damage/mold in the interior.

The most expensive piece of which is interior paint.