Thanks for these tips, I'm definitely going to ramp down the ammo carrying enemies later in the set to try and choke the ammo count. I didn't think about the backpack too much but your right, should probably ditch it in MAP02, In your opinion, in a 7 or 8 map set, would MAP03 be a decent place for a "hey I can see a backpack over there but how the hell do I get to it?" type of elaborate sidequest and then maybe add a regular progression backpack around MAP05 (or 06 if it ends up being 8 maps overall)?
As for berserk packs, I hadn't taken them into account for my "health items rule" in this yet, not sure if I should consider them "normal health items" or not, I may look into modding them not to recover health as you said...and perhaps is a different sprite for them as well. Something more shpere-like.