Need help with a duplex purchase

[Brad Klock]

I am new to the real estate game and am not really sure if I am making the correct decision or not. I am attempting to buy a duplex for $30,000. I personally know the owner of the duplex (friend of my grandfather) and he has 3 homes (all duplex's) side by side. Obviously he wants $30,000 each and I was attempting to buy one to get my feet wet before jumping in on all three. I walked through the one yesterday and it is in great shape. He is very good about upkeep and has the furnaces cleaned every year and paints and cleans after tenants leave. The entire house also has a new roof and new replacement windows. My real question I guess is, I went to the bank today and I can get the $30,000 but I need 20% down plus closing costs. I do have enough money in a savings account to cover this but I am trying to keep my personal assets out of this if that is even possible. Also, the bank said my interest would be around 5%, which puts the prinicipal and interest payment at about $250 + taxes and insurance. The one side of the duplex is currently rented at $325 and the guy has been there for about 6 years and is a great tenant. The other side is vacant at this time. I have been looking in the paper and on craigslist and most duplex's around the area rent for $350-$450/side plus utilities. I don't understand all the numbers and figures you guys use but the way I see it is that as long as I can keep one side rented all year long I should be good to go and everything else is profit to put back into a separate bank account for a rainy day (or another purchase down the road). I am looking for some guidance and is this a good deal or am I missing something. The taxes are extremely low I believe they are like 700/year. Please help!