I've found the biggest factor is proper pricing.

There are a lot of factors involved in this decision and ultimately you have to decide what is best for you.

Like I said, this would be my first REI and I really don't want to make a big mistake on a deal, but based on the numbers I've come up with, this property would cash flow about $500 initially while the loans are being paid back, but should generate in the area of $1800 once the loans have been repaid.At this point, I would be willing to take on any positive income, but I'm sure there are factors that play into this that I know nothing about.

Your CapEx depends on many factors such as age of the building, location, recent upgrades, etc.

Snohomish County is a great area to invest, and the airport at Paine Field will be a major factor.

Condos can work, but it depends on a lot of factors. 

If it is an online auction there is typically about a 5% fee that is paid by the buyer so be sure to factor that into your math.

The first time you consider a rental, fear is a major factor. 

Before I purchase the land, I would like to know my total investment including building, so are there any cost factors I should take into consideration?

The basic underlying factors of large downpayments and higher borrowing costs by either homepwners or investors never changes.