Alien Archive has some guidance as to what gear to dole out to NPCs with class grafts (AA pg. 137 - 141).
For soldiers specifically:
Gear: A soldier creature’s gear selection depends on whether it’s focused on melee or ranged combat.
Melee: Heavy armor (item level = CR), advanced melee weapon (item level = CR + 1), longarm (item level = CR), and two grenades (item level = CR).
Ranged: Heavy armor (item level = CR), advanced melee weapon (item level = CR), longarm (item level = CR + 1) or heavy weapon (item level = CR), and two grenades (item level = CR).
Yeah its kind of odd when you look at it. I mean this is a time/setting period where churning out high tier laser rifles isn't like turning out +5 swords in pathfinder. Its way easier. There's not really a reason someone like Abdarcorp couldn't just outfit all their guys in tier 10+ stuff for the lowbies, and tier 15+ for the better guys.
As for your question of levels.
I would generally hold mooks at 1-3, basically new recruit trainees. standard guys would be 5-7 ish, veterans start at level 10. Elite at 15.
I actually dislike the notion of a bunch of level 20 npcs running around, historically I liked the notion of PCs and rare NPCs being the elite/elite. And throwing a bunch of 15s to make a group equal to a CR 20 is generally just fine. Maybe you throw in a mini-boss that leads the pack at higher level, but for classes I tend to limit the 'masses' to around level 15ish.
Yeah its kind of odd when you look at it. I mean this is a time/setting period where churning out high tier laser rifles isn't like turning out +5 swords in pathfinder. Its way easier. There's not really a reason someone like Abdarcorp couldn't just outfit all their guys in tier 10+ stuff for the lowbies, and tier 15+ for the better guys.
I wouldn't say it's easier, because when you look at the price the high level gun are really expensive and as a company i wouldn't want to waste that much money into grunts that wouldn't even hit with the thing when facing strong enemies. (Which is kinda dumb because you'd think you'd have better armor penetration value if you have better guns, but that's the problem with including armor as a evasive kind of defense instead of a damage resistance mechanic.)
I would generally hold mooks at 1-3, basically new recruit trainees. standard guys would be 5-7 ish, veterans start at level 10. Elite at 15.
That doesn't seem like a bad idea if we only take humanoid and basic alien species, but it start's getting problematic once you factor monster CR into the equation. If level 5-7 is the average guy, that would mean that the ''average Joe'' is as strong as a Huge Elemental, which seems kinda off.
Starfinder actually gives exemple of a elite soldier and that would be Aeon Guard Specialist, which is CR 7.
I think the real problem with level in d20 systems is that pc can reach unthinkable level of power and are expected to fight things that mortal we're never supposed to go toes to toes with.Things like colossal red dragon and Kyokor should be met with magic, heavy artillery, tanks, fighters, mecha(just like pacific rim!), etc. I think that the idea of having a man-sized humanoid fighting and killing something as tall as a building with a sword or a pistol is kind of silly. It would be fine in a super hero setting, but in a space fantasy or a medieval fantasy it's kinda weird. Which is why i generally prefer alternative systems like E6 or E8.
In all in universe logic, the elite troops of a space nation should have the very best equipment money can buy, but the Alien Archive does give the example of such soldiers with the Azlanti Empire and, despite supposing to be really high tech have really weak gear if you compare to what is available on the high end.Anyone got any guidance ?
I'm gonna give you the advice i actually hate, and i apologize for that but; tailor your encounter to the PC. If you need an elite military squad to fight your pc and you need them to have bigger gun, find some for basic reasons for it and call it a day. Just pick weapons that would be appropriate for the challenge you wanna give to your player. I know this kinda gives MMO feel where ennemies are expected to be around your power level, but Starfinder wasn't made to be realistic, it was made to be highly cinematic and to have a fun gameplay. There's some other games that would emulate realism in a better way, but then they themselves have some other problems, like playability and complexity.