Well, we just added "recommended (highlighted) stats" in the character screen in the latest update.
As a general rule: build your team with 1 tank, 1 support, 1 attacker, and 1 flex (usually another type of support or attacker). In the character skills menu, there’s a highlighted damage type in the default attack description, and this helps you decide which type of ATK to build.
As for gear sets, some of them are thematically based around certain characters, so starting with those is a good idea.