@Josh Weber said it - good tools, good processes and automate as much as possible but also leave room for a personal touch.

I lived here for 2 years before buying my second house and rented out each of the rooms.

I understand that rent price is a huge factor, but there is only so much room you can lower it before all you attract is the wrong crowd. 

I've done some rehabs to make it livable, but I'm finding it a bit challenging to rent out as a 6 bed, 2.5 bath house, whether as a whole or by renting out individual rooms.

For inspiration "The Only Woman In the Room" by Ashley Wilson 

So, give yourself enough room to cover future increases with how much rent you charge. 

Should I rent it room by room while keeping the residences separate?

I wanted to see if anyone has experience with rent by room?

First question is if I have someone who is planning to rent out a room in the house and have a signed lease agreement can this be used towards the income to purchase the house?

Fresh landscaping, new paint, new layout, add a bath, a room, a garage, finish the basement, new roof, kitchen etc are just some ways to add 20,30,40K to the value with sometimes minimal investment.