First you have to make sure your zoning allows for a DADU and what the setbacks are. 

But you'd always want to talk to the city right away (or county) and find out the development standards for the zoning that the lot is in (what are the setbacks, height limit, min lot size, etc).

Running a foul of all kinds of local zoning laws is just the beginning.

From my experience buyers typically prefer these lots because they will not have any neighbors directly behind them.I can't tell from your question if there is an existing house built, that you are purchasing, or if you are buying a lot and going to build on it.Also, you should have access to an interactive flood plain viewer to look where the 100, 500 and zone X for the flood plain are situated.

@Kevin Hausfeld   Nothing would prevent you from building another home on it, assuming there are no zoning/building restrictions for 2 homes on one lot, but you couldn’t get a loan for it.

If I get red tagged (I think unlikely), I may reach out for guidance.   

Are there any red flags I should watch for?

Albemarle county tends to have pretty strict regulations when it comes to zoning and building.

Is the property zoned / approved for such a house?

That's the flood zone stuff, or stuff where value is less than what is owed, or maybe partials, land locked, drainage ditches, stuff like that.