That subgenre of Blues would roughly be called "Urban Blues." When referring to acts who recorded at Chicago record labels (Chess, Checker, Cobra, et al) it is knowns specifically as "Chicago Blues."
I would recommend you seek out The Chess Blues Box to sample a variety of some of the best post war Blues as a jumping off point.
Yup. The version I linked above is the one that I bought about 3 weeks ago. This release is just one 180g LP. Picked it up off of Amazon for about $20. I'm not necessarily an audiophile, but, to me, this record sounds amazing. It has a really clean, full sound with very little noticeable surface noise and popping. It's honestly one of the best sounding records I own and I highly recommend it if you're looking to get another Son House record.
I love that Stack O'lee track. I had no idea Bussard had a copy but I can't say I'm surprised. I got The Stuff Dreams are Made of a few years ago and that song really stood out for me. It's a great compilation of the worlds rarest 78's.
"Violin Sing The Blues For Me". 24 tracks from early blues bands and singers, including "Peg Leg Howell & His Gang, Mississippi Mud Steppers, Cow Cow Davenport, and Kansas City Blues Strummers. Amazon has samples.
Absolutely. I'm not at all religious, but his religious songs are amazing. Dark Was the Night is $7 on amazon.