I used them because of both the name recognition and the heroic sound to the theme.  Flash Gordon is about as perfect a heroic theme as you could get.  Like the film, it seems cheesy on the surface; but, it works beautifully.  I love its use in the opening credits, juxtaposed by Alex Raymond's amazing art from the strip.

Some of the tracks are from 90s/00s surf and instrumental bands, like Man or Astroman and the Ghastly Ones.  After Pulp Fiction came out, there was that 90s surf revival/surf-punk stuff (plus other rock instrumental groups and artists) and I got deeply into a lot of that:  Los Straitjackets, Man or Astroman, the Bomboras, Teisco del Rey, Shadowy men on a Shadowy Planet (The Kids in the Hall band), the Ghastly Ones, Laika and the Cosmonauts, The Tornadoes, Dick Dale, Link Wray and some others.  A couple come from the Heroes & Villains CD, from The Powerpuff Girls, with Shonen Knife, Mark Mothersbaugh and some others (including Jim Venables theme).  Rob Zombie provided a few and a few came from the compilation Saturday Morning's Greatest Hits, where 90s music acts covered old cartoon themes and songs (including the Butthole Surfers' cover of Underdog and The Ramones doing Spider-Man).  Iron Maiden gave me some, Black Sabbath, Judas Priest.  I have a CD of DC Comics-related themes, in original recordings, including the original Super Friends march, from Hoyt Curtain and the John Williams Superman theme (as well as the Wonder Woman tv show and "Molossus," from Batman Begins).  A few things came off the Life on mars and Ashes to Ashes soundtrack albums, from the British detective/sci-fi/supernatural shows.  My CD compilation aslo has sound clips of Gene Hunt (Phillip Glenister) , from those shows, but, I couldn't find the specific clips on Youtube.

Rob Zombie briefly had his own label, Monster-A-Go-Go, which produced The Ghastly Ones' A Haunting We Wil A-Go-Go and The Bomboras, as well as a couple of compilations (including a great Halloween one).

I had a much longer 1st draft set of discs I did that included a lot more, including more classical pieces, like Tocatta & Fuge, Verdi's Requiem, and the 1812 Overture.  That felt like sections went on too long; so, I edited it down and substituted some things to make the theme stronger.

As far as the recognized themes, it was more the sound, than the hero represented, in terms of my story idea.  More those kind of archetypes.    The main POV character I had in mind was a teenager/20 something, who becomes a sort of Trickster rebel, ala Harlan Ellison's Harlequin, or Zorro or the Eppie Thatcher version of Grendel.  He finds a mentor, who was a Batman sort of wealthy playboy/street vigilante, who was badly injured in the war with the villains.  He stumbles into a hidden base for that retired hero and takes refuge from the authority's security forces.  My basic idea was that a Luthor-type of villain was able to unite everyone to ambush and overwhelm the heroes, killing off the big gun archetypes early on; so, like Superman being targeted first to get him off the board and demoralize the other heroes.  Then they hunt the survivors down, killing them or driving them in deep hiding.  Then, the villains turned on one another, with the Luthor type emerging on top and subduing the bulk of the other villains, except a select group, which control different personal empires, while the Luthor type rules a fascist state.  The vigilante trains the young trickster and helps guide his attacks and recruit other heroes in hiding, after being guilted into helping.  He also has a daughter, who would be the love interest.  His conglomerate is still a major player, as part of the idea is that some conglomerates bankrolled the villains, to join in the spoils.

Every time I started trying to write things, I either barely got going, then couldn't get back to things or I would decide I was copying other stories too much, or I had trouble constructing a logical sequence of events.  I was wanting to make comments within it, about young people taking responsibility for the world they live in and also confronting their elders with the world they are leaving them.  Also, about the responsibilities of leadership and the fickle nature of hero worship, where people build them up, then tear them apart.

Maybe when I can slow down a bit I'll take another crack at it.  I was aiming at a YA audience, as I thought that would be more receptive to the themes, though it could work as adult sci-fi, of I can ever get a firm structure and work out the bad stuff.

The music, though, is stuff I had on CD, in some form.  My collection is largely rock, with mid-late 70s to mid-late 90s the majority, plus 50s roots rock, 60s stuff, rockabilly, surf, rock instrumental, some 50s & 60s jazz (especially spy stuff), Classical, some bluegrass, some disco & funk, good bit of heavy metal, a bit of R & B, punk, ton of New Wave/Post-Punk, bit of Prog Rock, movie soundtracks.

My tastes are probably the most eclectic in my family.  To illustrate, I was once helping out at another Barnes & Noble, in St Louis, which had a music department (we didn't) and bought three "best of" CDs there:  Twisted Sister, Booker T & the MGs, and Petula Clark.  I like a lot of "epic" sounding stuff, like Queen, Meatloaf & Jim Steinman, operatic pieces, Morricone, John Williams, Michael Giacchino, Korngold, Pouledoris, Zimmerman (some, but more and more his stuff sounds the same).  I like strong, well trained voices, like Julie Andrews, Petula Clark Dusty Springfield, Pat Bentar, Bonnie Tyler, Karen Carpenter, Toni Tenille, Shirley Bassey, Judy Garland, Dionne Warwick.  Picked up a lot of music influences from movie, tv and cartoons......Carl Stalling probably gave me more appreciation for classical music than anyone.  My mother was a music teacher, at one point, and exposed me to a lot of showtunes and singers like that.