All of them are fair and legal and will all have a spot in your funding options "toolbox".

Just want to point out that F,L & S is not legal everywhere.

Looking at a triplex and the ad says "unit is legally a duplex". 

You need to consult a local attorney and have them guide you on the correct way to "wholesale" if its legal in your area.

ALSO- The property I am looking at looks like it could generate about $80k profit for the LLC... would that be legal?

So legally couldn't spend the money anyway, so I've got a safety there lol.

I'm not sure I understand the question, but as long as you give the current tenant the legally required length of notice for the non-renewal of the lease, after they move out, someone else can move in immediately.Edit: if it's clean and move-in ready

We'd legally rent it back from January 2019 through May 2019 and be moving out of state turning it back into a rental.I'm not looking for "that's a bad idea" - I'll come up with those conclusions on my own .  

In most State a mailbox would not be enough as you need a person to receive service of legal documents..

Ideally, you should find one that has experience dealing with medical/dental offices since there are some practical considerations to think about on the legal end.