According to Records screen both Envoy Grade B and A require you to recruit 13 members. But B triggered when I got 13 while A didn't so I guess it's just description for Envoy Grade A that is wrong. Edit: Envoy Grade A triggered at 14.

You'll likely unlock most of the features by playing the game normally, but this is here in case you want to know specifics -Solo Hero achievements Set your party members, monster party members, and boss party members to inactive, then start a new mission. If you add a party member, then you won't earn any solo rewards for that mission. You can still use prospectors and H.D. Creations -Mastery Clear level 10 -Base camps Clear level 20 -New mission Clear level 30 -Affinity Start 1 new mission -Extract...

Does it cap at 999?

How to get the "Fallen Star Gems"? Would be nice if you see in the description how to get the ressources.

"Novice Hero Grade F" record requires 100 attack according to description, so should be earned very early, but even when hero is at 1000+ attack when farming level 28 it is not activated. Edit: either game restart or switching locales (or maybe just writing this post thanks to Murphy's law) actually fixed the issue and I got both F and E records without doing anything else....