They are not requiring me to assume the mortgage, I just really want to get that low interest rate.

For tax purposes, the LLCs are disregarded entities, and all income and expenses are reported under the holding company. 

Based on info provided, rate should be more in the mid 7s-low 8s likely, back of the napkin, with no lender discount. 

IF I'm going to make extra principal payments to pay off a "low(er)" interest rate mortgage early (compared to today's rates), my gut reaction would be to pay off the highest interest rate mortgage first.

With 1031s - DSTs seems like a possible approach since it's truly passive however returns are low. 

  $850 is way too low to accept.

I have never seen a hard money lender have great interest rates and low points.

Don't forget Nazz Wang BP Episode 148 BiggerPockets Podcast 148: From 0 to 51 Units Despite Living in a Crazy Expensive Location with Nazz WangI also recommend @Dawn Anastasi's e-book on Milwaukee areas to start. 

They have auctions starting as low as $1, some with no reserve.

You could save enough in taxes to offset all your living expenses.