- Why :
The way Artemis works now is not according to the rules. If I upgrade to Artemis it costs me 750.000 C-Bills (500k for Downgrade), whether I have 1 or 6 or even no Launcher at all. So I have to pay for just the Possibility of me equipping Missiles. I'm sorry but that's not really well thought out. With FF, Endo and DHS I can understand the price tag, because you (nearly) need to rebuild your whole Mech, but Artemis is just a piece of equipment placed alongside a Launcher.
The second thing is that If I upgrade (or Downgrade), I upgrade all Missile Launchers at the same time. This is wrong! Yes, if you add Artemis to 1 LRM Launcher, all LRM Launchers must be equipped with Artemis and same goes for SRM. But according to the rules I could have 1 LRM with Artemis and 1 SRM without Artemis and vice versa. With your System I can't.
- How :
I would create 2 Upgrades. "Artemis LRM" and "Artemis SRM" for 0 C-Bills (or make it a really small number). What they do should be easy to figure out

2. Ammo :
- Why :
The Price of Ammo is a balance mechanism, no doubt about that. But your current rearm system is to easy to exploit. The initial cost of Ammo shouldn't be the final cost. If I just need to grind my way the most expensive stuff I can dream up and then drive that without penalty, it becomes meaningless. You want to give players a 75% discount? Fine! But don't give away 75% for free and then ask for the full price for the rest.
Imagine yourself walking into a grocery store and whatever you have in your cart, 75% of that is free .... would you pay for the rest or would you just take the 75% and go home?
There is no difference between careful aiming and don't wasting shots, and plastering the landscape with wasted ammo at the moment. I feel like I'm not being rewarded for conserving my Ammo.
- How :
There are actually 2 ways do it right and fairly. Either you do it like you already do with Equipment, that is paying only a fraction (25%) of what is damaged (used), or just reduce Ammo Cost to 25% and have everyone pay for every shot they used (100% of 25%).
Shouldn't be too hard to implement.
With kind regards
Nighthound