Character creation has just a few simple rules. Yes Space marines are tantamount to demigods but they still have limitations both physical and mental. As far as creating a space marine goes, even a junior one, There is obviously the expectation you are already well above the average. That's fine, just keep it within a reasonable sphere of power. TLDR don't try dueling chaos lords or Drukhari archons and we should be fine.
Character Creation Sheet:
Name: if this has to be explained to anyone than I am sorry, there is no hope.
Age: As you are all newly minted scouts you are all around 19-25 years old. But still superhuman in proportions of raw intelligence, reflexes and boosted strength.
Appearance: Pictures are fine here, no anime is all I ask. A written description is fine as well.
Equipment: Scout carapiece armour is a given for this. And the bare minimum scout loadout consists of grenades, a bolt pistol and a combat knife. With a group this small I would rather not have everyone in the squad take up a sniper rifle and special weapons. & remember loadouts are expected to change with each deployment so don't get too attached to the idea of one specific weapon. There's nothing wrong with picking up a standard bolter or going bolt pistol/combat knife. The classics are classic for a reason.
Psychological profile: I honestly don't expect or need much here. Don't make your character too much of a lone wolf to the point where I and the other players have to waste time convincing you to join the game and we should be fine. Being a team player is something scout marines must learn to do.
As a visual reference. Here is a scout marine armed in their typical panoply of war.