There isn't official guidance on Shadow per adventure as it will naturally differ based on the adventure type - a diplomatic quest to the Grey havens will be low/no shadow while a descent in to an undead haunted old fortress in Angmar will have lots of Shadow.
I tend to go light on Shadow until the PCs have wisdom or valour at rank 2, then its open season.
This is for two reasons:
1) Theme: earlier heroes tend not to be taking on frightening/magical challenges and it lets me introduce a growing threat from the Shadow.
2) Mechanics: starting heroes are very likely to fail Shadow tests even if they spend hope, as they're 1d (2d with Hope) against a TN of generally 14-18.
Once they've got wisdom or valour at rank 2, they've at least had a chance to get a virtue that helps with these tests, or bought valour to rank 2 to help against Dread tests.
You can see a similar philosophy in the official materials: here's a spreadsheet with a summary of the Shadow gains in Tales from the Lone Lands.
https://docs.google.com/spreadsheets/d/ ... sp=sharing
p193 for the Shadow reducing event. Similar examples crops elsewhere in other materials, such as returning a dwarf's remain in Moria or meeting Arwen in Rivendell to remove a Shadow scar.