How do I know the vacancy rate / how long it took to find renters for comparable properties?

It's just not clear what you are actually doing here. 

Does it need to be converted back in to a rental after your 2 years to qualify for a 1031?

If they do a great job, $100 is a great deal. 

For bookkeeping it depends on your portfolio.A portfolio of 1-3 SFR's can likely be a DIY project.For 4+ you may want to consider outsourcing.For tax prep, you'll likely want to have a pro handle it regardless of the portfolio size.

Have you asked your other agent?

Don't make your life more complicated than it has to be.

Vaughan, did you tell him he said he would do it for free?  

Here’s why selling your primary residence to your LLC and then renting it back isn’t a good idea from a tax perspective:Self-Dealing Doesn’t WorkFor tax purposes, a single-member LLC is considered the same as you, so paying rent to your own LLC is basically just paying yourself.

If you do the math, since your borrower is paying interest on interest, it raises your effective interest rate by about a point.