Thanks for trying out the game and giving feedback!
DNA Types - We'll have more information provided in-game on the types eventually. Here's a quick rundown for now. Base DNA is 1 positive 1 negative with a medium chance to mutate. Volatile is ~3 Positive and ~3 negative with a high chance to mutate. Fortified is all positive with a low chance to mutate. Paramount is "Boss DNA", which for now just provides a large amount of stats but hopefully eventually will provide a boss mutation.
Transmitter Arm - Some rare mutations will have a balance between being more useful against Solus or Prism, but I agree this one still needs a bit of balancing and we'll make the tooltip more descriptive.
If you're having trouble finding weapons, look for the Stockpile Waypoints on the map (Yellow Ammo icon). The weapon variant not being able to be picked up is a glitch in the current build along with mementos being un-inspectable. We'll have it fixed in the next update! I fixed the issue you mentioned with the sack feet thighs as well just now.