For years, I had thought that "National steel" guitars were exclusively metal-bodied, and that the similar "Dobro" guitar often used in country music were always wood-bodied. I now know that it's not that simple; in fact, the whole mess is too complicated to go into here and now. There are several whole threads on the subject of resonator guitars you might find enlightening (even though you're not a player); one of the most recent was entitled something like "Oooh I want that stainless steel guitar."

"The Blues" can be defined in many different ways, as a very broad category of music or in a very narrow and restricted sense. The various responses appearing within this thread represent a number of different ideas about what music is "really" the blues. You'll have to decide for yourself what it means to you.

There is an old African-American tradition that draws a strict line between gospel ~ church music ~ and blues ~ the devil's music. I've never been able to hear that much difference between the blues and good soulful Black gospel music. (Of course, the lyrics differ.) There are a number of artists who divided their career into separate church-music and secular periods (Thomas Dorsey, Sam Cook[e], Al Green), but then there are others who always included blues and gospel in their repertoires at the same time (Fred McDowell, Gary Davis, Blind Willie Johnson).