Personally I'd go for it, but I would rent both sides out until I had rebuilt your cash reserves from the construction. Depending on if you have to have a new line pulled from the road for power, the power comp could charge a lot, plus having to put in a new breaker box and split the two sides could add up quickly...
My only thought is that if I buy soon I still qualify for the first time home buyer credit. But to apply for it I would need to live in it "most" of the time for 3 years which is possible but not ideal.
I have a two friends that did this (it was awhile back so they didn't get the credit). One was single and he made out like a bandit. He still has the place (doesn't live there now) and all it does is make him money. The other guy was married, had a kid while living in the duplex and wound up selling it to "break even" and get his own place for his new family - he hated it. Turned out the second guy rented to somebody who liked attention and was constantly calling him about house issues. Most of this stuff turned out to be nothing, but he felt he should do the right thing and keep up the place the right way. If you don't always plan to live in the area this might be a problem.
As to the updates, you may want to check zoning regs to find out if this is allowed, also since you rent there, maybe there are association fees in this community that you have to figure in.
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