After framing out the access to the room from the kitchen, I added some dry wall and voila - my 4/3 is now a 3/2 with a STR studio.

•I live in the basement and rent rooms, earning around $6,500 monthly.

Unfortunately, the smartest people in the room have braced for it. 

Some hosts have found that more bathrooms are more attractive than offering a large living room, but I think it's somewhat market and guest avatar specific.

Are there specific amenities that are particularly attractive to rent-by-the-room tenants?

If you try to hit a home run or grand slam, don't be surprised if you strike out.

You will probably be a little negative on cash flow unless you rent by the room or buy the interest rate down or both, but honestly a little negative on cash flow isn't a big deal if you still have most of your cash in the bank since you only put 5% down. 

@Jorge MartínezIf the builder is offering incentives to buy down your interest rate and if there is some negotiation room on price the new builds can be a good investment because you'll have a lower monthly payment and new builds usually come with some type of warranty and will have lower maintenance cost because everything is new.

Then surprise her with request to have her show you her kitchen, bathroom and living room. 

Mine are all in Grand Prairie, Arlington and Fort Worth in C+ class hoods.