Bought 1/2 of the duplex should I buy more?

[Allen Clark]

In December I bought 1/2 of a duplex in urban Seattle. . 

Purchase price: $350k
Size: 1,100 sq ft
Mortgage + taxes + insurance: $2,000/month 
Down payment: 30% = $105k
Age of house: 8 years
HOA: $0 - no HOA at all
rehab $$ spent: $0

Beginning in January I have been getting $2,750 in rent and I am sure I can get more next year when the tenants flip. I will go for $3,500 and see if I need to move down. This house has been brain dead easy and it has been cash flow positive from day 1.

We have the 1/2 of one house. When these were built the builder constructed 4 duplexes total. All the duplexes have no HOA for a total of eight units. I've talked with the owner of the other 1/2 of mine and I am set to buy that if we can come to terms. He is looking to sell in the summer of 2016.

My question to you is should I buy more of these? There are eight total and the prices are rising here (but so are rents). I can see why I would want to own both halves of my house so I can take care of building maintenance. If I buy parts of the others is the lack of diversification something to worry about? The units are right across the street from a small university and within walking distance to Capitol Hill ( very trendy) International District (like China Town), sports stadiums (go Seahawks), etc. This locations rents very well. 

Should I be looking to ultimately buy all eight or is that too much net worth to pack into one small street?