Advice for buying property in a historic district

[Michael Weis]

Good Evening all,  I am currently on the hunt for my first buy and hold rental property.  I came across what I think is an awesome side by side duplex, 3 bed one bath 1500 SF per unit.  The home was built in 1900 and is in a historic district.  From my own math it looks like I would clear minimum $600 per month cash flow and possibly up o $1000 per month if I were to hit a grand slam on the deal.  The house does need some work mostly on the interior.  It currently has a metal roof and I am uncertain of the condition currently.  Looking for some advice on dealing with historic properties.  What are some hurdles I may face?  Will the not allow vinyl replacement windows and things of that nature?  Thanks.  

Mike