I know that I should look at square footage, bedrooms, and bathrooms, within a .5mile -1 mile radius.

I would do that to have a lower monthly payment, which equals higher cash flow.I'm also in the same boat as you, searching for a 2-plex to a 4-plex, I haven't been able to find anything good cash flowing properties, but it seems like the 4-plexes in my area (Vancouver, WA) are cash flowing slightly better than the 2-plexes.  

There is a tax lien auction coming up in Seattle. Does anyone have experience buying at these auctions ?  My questions are what kind of properties come up at these auctions?  I have an idea to use small "useless" lots...

First sf is square foot.Second, let's say you do all your figgering and guesstimates on a faux cap rate. 

Thanks for the mention @Brian GibbonsI just sold a listed house here in WA.  

I'm considering buying a house in DC that's roughly 1000 square feet, but 400 of those are unpermitted.  

I work at Weyerhaeuser and we have timber holdings out that way.If I were you, I would join the Washington Landlord Association, at walandlord.com.  

I need a forced hot air furnace for a well insulated 900 square ft row home in the kennsington area of philly

Adding additional square footage to a flip is a time consuming and costly option best left to someone with construction experience.

If you owned a few square blocks and it was close to town?