They seem to do seller financing a lot.

My plan for this year is improve my credit, get my real estate license (to increase my income on top of my W-2), possibly career transition into the property management space (to learn more), and save as much as possible and learn as much as I can.I’d love to house hack close to home but my area is so expensive it seems like it’d be close to impossible. 

Seems like easy savings. 

The units are being rented below market at around $1,700/unit, whereas market rent seems to be around $2,150/unit for these 2 br/1.5 ba units with laundry in each unit and undercover parking.

We both have good credit but my lender made it seem like there was no getting around putting less than 25% down on an investment property.

Does this kind of increase seem reasonable?

It seems investing in TN where we are now, and being able to work on the properties ourselves makes more sense.  

I'm hoping he'll have some options for me.I know a Home Equity Loan is basically a second mortgage in normal situations, but they seem to come with less red tape from what I've found.

As others pointed out, there are overlapping features, so does not seem it's worth it.

Austin area seems like a cool techie area with good rental demand.