I own a duplex in the area and I think I know the exact house you're talking about, over on Troy street.
Sellers are taking advantage of the market, and I'm of the opinion the upper/lower duplexes are priced out in Ferndale. I ran the numbers myself on that duplex and the cash flow looks negative to me (just like all the other duplexes in Ferndale right now).
I strongly suggest you create a spreadsheet so that you can crunch numbers quickly as you peruse through properties. It will safe you lots of time in the long run. It blows my mind when people buy investment properties without having a VERY good idea of how much money they will net.
I'm not a fan of forming an LLC, especially if you only own one house. Your landlord insurance will have liability coverage, and if you're really worried you can up that as high as you like. Eventually when you buy more properties you should get a PUP (Personal Umbrella Policy) for even more liability coverage.