What concerns should I be aware of that are common with duplexes?

One concern I would have is the durability of those rents.

Anyone else concerned with the debt crisis?   

Im less concerned with actual areas and just more interested in trying to figure out the best size of the property as I always hire property managers.

My concern is you're going to get yourself tied into a contract and be financially liable for something that you're not ready for.

My portfolio has performed beautifully for me in the past but I’m concerned about a future SF earthquake and wondering about the opportunity cost of staying in San Francisco relative to investing elsewhere.

My primary question I seek to have answered by posting this post is fairly straight forward, yet I encourage debate concerning metrics and comparisons.  

You also have to be concerned about debt to income ratios as second loans usually carry higher interest rates and shorter terms (think larger payments). 

My concern would be that if I let them move in to finish it, then I could not get them out after and would have a lot of legal issues.

My concern is that I may only have 2 weeks to cancel my offer.