@Meng Long think about it this way when looking at deals...
if you are willing to pay the rest of the mortgage, considering you are buying a duplex, then most likely the renter after you will also be willing to pay that rent. But also take into consideration though that if you aren't living in San Diego three years from now then you who will manage the property? that will significantly cut into your cash flow if you have to hire PM.
I still think the VA loan is something to take advantage of but signs do show that the SD market is slowing down and SD is a cyclical market historically, meaning what goes up will come down. ultimately, if you are buying for the long run and plan to keep this place for 20+ years then don't worry about cycles, just buy smart.
Feel free to send me properties you are looking at and Id be happy to help you run some #'s or connect you to a agent i trust to help you get into the right property.