For the most part, commercial seems a bit more complicated than flipping an SFR contract like this. 

Hello Maura,As long as your loan is presented and structure properly up front the UW should be able to figure out what you're doing quite quickly.In my opinion 60 - 90 days is unacceptable unless you have a really complicated file or the customer is really slow in getting the Loan Officer what they need.Find an LO that knows what they're doing and you should be able to get this done in less than 30 days 100% of the time. 

I didn't want to complicate the HELOC application, or screw up a new conventional loan app, by trying to do both at once, and the closing time is pretty much the same, so buying with the equity line cash is pretty much a done deal for now. 

(in retrospect it was likely because his commission would have been complicated). 

Pretty easy to get along with, the money showed up at the closing table on time, and the draw process wasn't too complicated.

They're not that complicated...or expensive.  

The important thing is to get started, don't over complicate things in the beginning. 

What are the complications, legal ramifications, additional expenses, pros cons, of instead of dumping money straight in, having a partner make the LLC take out the loan.

These are more complicated and the fees are much more than a standard Forward 1031 Exchange transaction, and some Qualified Intermediaries do not administer them. 

They ended up with medical complications causing them to move out in less than a month.