The tax lien (also called a fifa) exists prior to the tax sale and is recorded in the county's lien records - it's an unpaid debt secured by the property.  

A mortgage is then filed against the property to secure their investment.

I was thinking about being a real estate agent, but I'm missing social security number, so I can't be qualified as one.

Require a higher security deposit, last month's rent, both?

Your method makes sense for my higher rent units, but I'm not sure if it makes sense for lower rent units, which I'm already requiring first, last and security? 

If I have a tenant move in mid month I always collect a full first month's rent at move in (along with the security deposit).

The question, I  am trying to resolve is moving the property (albeit an investment property) from one owner to a multi-member LLC as it opens up the ownership to multiple people who were not part of the original loan package.  

Aside from that, they're usually much safer than an apartment and offer more security.

I have a good paying, secure job making 6 figures and I don't spend much money.

If you live in Sandy and have a duplex in Midvale its easier than having 2 single family houses in different locations say Cottonwood Heights and West Jordan.The final part I would bring up is Multifamily units will be easier to be used for portfolio loans in the later games because it meets the physical definition of packaged real estate.