There are many similarities between this deal and one I did that went VERY badly... the only difference is the family member aspect... which could make this better, or much, much worse.
Things that this deal has going for it.... the recent updates... one of the major downsides to the deal that went bad for me was improper maintenance allowance. I also like how you calculated 8% even though its full right now... without knowing more about the market, I'd say that's a good starting point.
One problem is that the rents are at the top of the market... I'm in the same situation right now... I see the leases, the units are full, but is that a fluke? A fix for this is to do your own market research, come up with what you would ask for them if you were starting from scratch, and do the numbers from there.
Now, financials... I put 25% down, 6.5%interest for 30 years, since that was a quote I was given recently... that's a monthly PI payment of 1,300 or an annual payment of 15,600. So, you would be losing $200/year. Also, I do think all of your numbers are good except the management. 10% of gross is reasonable, but after a year, if you find a manager that can charge you only 10% without any other fees or costs, I'd be surprised. Even if you could manage it yourself, I don't think you would be getting paid well for your time and money.
Summary: At the current terms, it does not make sense to me. I would never advise you to even get close to a negative cash flow deal. The value in the land is significant, but only if you can act on it. Unless you have a strategy in mind to access this value and the means to accomplish it, you can't consider this value. I think your uncle will understand.... or maybe lower the price further... you never know. Any ill-will felt by turning him down will be far less than the ill-will when you loose your shirt on it.