Tried this out recently, very fun! It would be good to have a purpose made scrap weapon button so I can salvage ammo for one held with similar ammo.
Also I found an interesting bug wherein if I drop a weapon with the usual drop key, then pick up another, I can still pick up the one dropped and now can hold both.
Lastly, the enemy pack is not working either alone or with Subsonic.
I was using Uzdoom 4.14.3.