@Su Lee on the topic of a solo 401k, not everyone qualifies to have one and maximize it to gain the maximum contribution.

I cash flow on my first duplex an amount I am comfortable with and I will cash flow a comfortable amount with this other duplex.

I talked to my girlfriend and we are heavily leaning towards a multi family to reduce costs and maximize delayed gratification.

Having your own source/relations are much more comfortable to me, I will definitely contact her.

If you think you'll only do it say, 5 times, then wouldn't you be better off (comfort-wise) just renting out the non-rehab rooms while living/rehabbing inside, which is sustainable?

I may eventually consider investing in a long distance market, but I think I'd like to get my feet wet locally so I get comfortable with the process in a place where I have more resources and access.Does anyone have any suggestions on what markets in the general Portland area can potentially provide cash flow through single family rentals?

I would be comfortable trying software with just a few vanilla rentals. 

Second, I hope to delegate as much as possible, for maximizing the passiveness of my income structures.

@Kelsey Mortimore find deals that you are comfortable with, even if there is a drop in RE prices. 

Usually that comes at a price of a lower commission split. 80/20, 70/30 or even less % to you until you feel comfortable.