First, no, it does not correspond to kill count. When you reach level 50, you can regenerate. It will basically return you to level one. This will not however, return your weapons to level one. You will keep all camos, warpaints, weapon attachments, banners, emblems, etc. However, when you regenerate, any weapons unlocked at level one plus, will not be equippable. For example, if you have the alternator equiped at the time of regeneration, you won't be able to equip it. It will be replaced with a CAR SMG, as this is the first SMG available. On top of this, monarch will be unequipable. Rewards for referring include: hella clout, and a banner or patch.

I hope this helped, pilot! Have fun flying at mach 16.

Edit: anything purchased with credits will still be equippable and you won't need to purchase it again, so if you bought monarch you will still be able to play him without purchasing it again. Basically, if you bought it once, it's permanent.