Depending on the property far more than the acquisition price may be required and that will also dictate the best loan product. 

You can probably find some around DFW in some of the outer cities for around $250,000, so 1031 the ones with the most equity into more properties with chances for more appreciation.One thing I would suggest is not to buy NEW from the big production builders. 

.- Working a W2 as a firefighter, posting and consuming content- Leaving my W2 to dive deep into real estate investing and working as an agent... and still watching/posting content all while business was ok - Deleting social media apps (one have one on my phone that I use 10 minutes or less a day), diving deep into building my business and skills which have drastically increased due to pure focus and increasing my business significantly- moral of the story... focus on the things you need to do in business (dollar productive activities) and life experiences while reducing consumption will increase your success  

I know there are hundreds (thousands probably) of lenders out there that offer a DSCR product.

We have a 30Y Fixed DSCR product that would likely fit your needs. 

For walls in common areas like halls and stairs, there are rigid products that can absorb some sound.

I wonder why they don't make roofline sprinklers or some other product like that. 

When you go to a Bank or Credit Union, they can only offer you what products that bank or credit union offer. 

Freddie has a reno loan product that can be used for investment properties; this is only for first position, though.For the Heloc - it goes back to whether your mom wants to continue carrying the loan for income, and if so, how will you pay off the heloc once the rehab is complete?

Small shop brokers that have access to multiple programs so that they aren't beholden to one or just a few loan programs will typically get the most competitive product for the borrower.