I have no background in real estate investing beyond a few books I skimmed but am very eager to learn.

It sounds like you have a good background for getting into real estate.  

Question for all of you buy and hold investors: Would you prefer to buy a single/duplex/triplex (not counting apartments) with existing tenants with good profiles (credit, background check, etc), or vacant so you can find your own tenants?

@Ronnie Boyd   that part of Oregon is a beautiful spot.

Also if someone has a document they can reference that provides solid background that'd be awesome too......perhaps to frame the above conversation.---  Some of my questions are related to:-Difference in rules between 1 property per year, and 3 per year seller financed, as an individual, or as an LLC, and what happens with multi-member LLCs and who's "count" those properties applies to-Whether Dodd Frank applies to raw land, improved land, properties the buyer is not planning to owner occupy, etc. and if any of those are exempt, what paperwork I should have the buyer sign at closing to state this.

Nice job thinning out that beautiful oak at the main entrance.  

My technical background helps me understand why it could build a great house.

I have studied investing (primarily stock market) for much of my life but have in the past not done a good job getting a base below me so I can really apply that knowledge in earnest. 5 years ago just after remodeling a home with stone walls built in 1900 with a naive understanding of what the costs and time inputs would be, the housing crash happening right in the middle of this, persevering and turning it into a beautiful home.....Then I was laid off.

Hi @Loren Thomas welcome to BP - I also live in Lake Stevens - I love the 2-4 unit's as well 30 year fixed rates are a beautiful thing. 

Sorry for the long background, but just wanted to give you all a sense of my RE experience.