I just wanted to save others some aggravation with these achievements since I could not find any information which could have saved me a lot of time and frustration.

• If you are trying for the Highlander or Hunter achievements, you cannot get the 100% in Normal mode achievement Quickening at the same time. I had thought that by simply using only the Haggis sword (lvl 1) and the original armor (lvl 1), I would still get the achievements, but after finishing the game this way, it is not true.
  
  
• If you want to go for the Quickening achievement, then this must be a different playthrough.
  
  
• If you want to go for the Highlander and/or the Hunter achievement(s), then that must be a completely separate playthrough (not 100%) where you do not pick up any of the different swords or armors. You may collect any of the other items, but not the swords or armors as apparently even if you don't utilize these swords/armors, it still negates the achievements if you collect them.

TL;DR: Highlander and/or Hunter achievement(s) - DO NOT pick up any of the extra swords/armors.