Ashardalon, the great red dragon, started as a background character and antagonist in the last chapter of an 8-module adventure series for Dungeons & Dragons 3e in 2000-2002. The first, last (where the dragon actually appears), and one other were written by Bruce Cordell. There do not seem to be any novels dealing with this character, so only the background information from the 8 modules would apply. The board game is apparently set after the adventure path.
Cordell is also the author of the Dungeons & Dragons 2e adventure The Gates of Firestorm Peak which is regarded very highly. The module should give you a very good picture of the Firestorm Peak. There is no mention of Ashardalon in that adventure, though.
One of your links in the question contained this history/explanation taken from The Draconomicon:
After suffering a mortal wound, Ashardalon attempted to extend his life by binding a balor called Ammet to his chest in order to function as a second heart. However, his injuries were too extensive for the balor's power to keep Ashardalon alive. He then moved to a domain in the Astral Plane known as the Bastion of Unborn Souls and established his lair there. He was kept alive thanks to the timeless nature of the Astral Plane and the unusual flow of energy that permeated the Bastion.
This wordpress site, Scholoars and Serpents, has an extensive summary of the background information and details from the modules that puts that very brief summary into context. Here is the timeline proposed there as a start:
Ashardalon ravages the world
His cult worships him as a god
Gulthias [cult member] makes Nightfang Spire his temple
An Elvish dragon cult builds the Sunless Citadel
Ashardalon destroys the druids
Dydd the Wise [leader of the druids] creates a new people
Dydd cuts Ashardalon’s heart from his chest
Ashardalon escapes to the Abyss
Gulthias brings the heart to Nightfang Spire
The Sunless Citadel is destroyed
Gulthias becomes a vampire
Gulthias travels to the Sunless Citadel
Gulthias is staked to the ground in the Twilight Grove
Belak the Outcast finds the Citadel
Belak helps the Gulthias Tree create the Twig Blights and lures adventurers into the Grove
A party of adventures release Gulthias by destroying the tree
Gulthias returns to Nightfang Spire. Centuries go by
Adventurers kill Gulthias
At some point prior Ashardalon infuses Ammet [a balor] into his chest
Ashardalon uses Desayeus’ totem to enter the Bastion
The Demogorgon wants to extract the balor from Ashardalon
The Demogorgon sends The Cathazar to search for Dydd’s ancestor
The Cathazar uses Dyson to open a demonic portal
Dyson is defeated
The soul sickness appears
The soul sickness troubles the gods
Dydd’s ancestor enters the positive plane and kills Ashardalon and the balor.
Ashardalon becomes a vestige
It also contains this quote from Dragon #365:
Few can ignore the legacy of the mighty red dragon Ashardalon. Ancient even by the standards of dragonkind, he was a force for evil in the world—his ferocity and greed was unmatched by any of his kin. Even when the great druid Dydd put down the beast, ending his reign of terror, Ashardalon rose from the ashes of his grave once more, bolstered by his wickedness and by fell pacts made with dread abominations. Although we can rest easy in the knowledge that the menace posed by this beast is no more (or so we hope), Ashardalon remains a cause of wonder and speculation.
The default setting for Dungeons & Dragons 3e is Greyhawk so the original modules are set there. They usually left setting rather vague, though, so it could take place anywhere. The first two modules were recently (2017) reprinted and set in Forgotten Realms.
If you are looking for painting advice, this BoardGameGeek list has all the monsters and includes examples from the D&D miniatures line to represent them--i.e. a painted example. Likewise, any entry in an appropriate Dungeons & Dragons Monster Manual or just looking online for each monster should give you ideas.