Is there a website or other source of information where I could start to get some basic knowledge on the US housing market rules and tax laws? 

The best lead source I ever found is propertyradar.com and it can do so many things for you it will take an hour to explain.

A very good source of local analysis is rereport.com 

What are the best sources to receive local real estate data I.e( market inventory, average days, median sale price, etc)?

How are you sourcing your notes?  

@Amanda PoltonYou should find a good investor friendly agent, modify your criteria, or start sourcing deals yourself for a duplex that makes sense for you.

My feeling is that they are growing fast, and eventually they could get greedier and bad things could happen.I started to look for other sources of information, so I came to bp.

There are plenty of competitive financing sources through non-conventional lenders that focus on investment property loans.   

Purchase price: $220,000 Cash invested: $25,000 Sale price: $325,000 This deal was sourced through our own marketing at Tree City Homes, so we knew exactly what we were getting in to.

Purchase price: $220,000 Cash invested: $25,000 Sale price: $325,000 This deal was sourced through our own marketing, so we knew exactly what we were getting in to.