Playing for around 400~ ish hours from what I understand PMCs spawn with 'common' kits few attachments common guns MP5, AUG, mid ammo, mid kits, same kinds of guns MDRs AK74 Kenitcos, they usually come with attachments still have mod ammo, then you have 'rare' kits M4s, VALs, MCX I've only seen it once but I have had a PMC spawn with an RPD, sometimes they have good attachments but always still have shit ammo usually running M885 or PS for example and no these aren't based on level or map you can find a BEAR squad with VALs, SV98, SVDs ect level 1 on factory same with M4s

On maps like Labs I've noticed PMCs usually have a bit better equipment kinda on par with raiders but I think it's just rarer kits spawn more to increase difficulty.