Music:
-it's just Valkyria Chronicles OSTs with a sprinkling of Napple Tale, Fable, Crystal Chronicles, and Mana

Sampled Footage:
https://www.youtube.com/watch?v=Wpvh9TmvcMg (the mobile game)

https://www.youtube.com/watch?v=52VJOhdiJuA (early valkyria revolution footage)

Citations:

https://web.archive.org/web/20160602000710/http://blogs.sega.com/2009/06/08/valkyria-fans-we-love-you/ (quote about VC1 sales)

https://www.eurogamer.net/valkyria-chronicles-3-denied-eu-launch (VC3 denied western launch due to VC2 sales)

https://blog.playstation.com/2017/11/20/valkyria-chronicles-4-launches-on-ps4-next-year-insight-from-the-producer/ (various dev insights)

https://web.archive.org/web/20090719102233/http://www.cinemablend.com/games/Valkyria-Chronicles-2-Announced-For-PSP-18672.html (despite VC1's sales, they wanted even better numbers through the PSP)

Foreword From The Lord of the Rings is shown

I can't link the artbooks for legal reasons, but they're largely available online, and comprise the bulk of development knowledge about the game. Most of wikipedia's development citations come from these art books.