two years into rental business now

Bought first rental house SFH in 2010 ($300,000 all cash offer). I am very excited to be able to get the 1st house after 20+ offers with no success. I learned a lot from the first deal and from TZLC at that time. My target is relative new property, no or minimum HOA, price in $20-30W, less maintance, can be less return, high appreciation potential. I have 9 properties (3 all cash, 5 loans, one in escrow now) now after more than 2 years and with a return of about 5-6% (with PM). I know the return is not good compare with other landlord's >10%. But, it suitable for a small landlord with full time job. I am planning to buy one or two every year for next 10 years and retire. Most of the houses I bought just over the internet/email without set a step into the house (remote), close at my house (mobile notary). It is good on line shopping experience.