I'm pretty amazed at how much has gone into this so far, really. On a similar note, while I'm not using FWE, I am using a series of mods that increases damage across the board for all weapons, as well as MMM at quite the full, fun, delicious settings, which makes most fights I pick a bloodbath if I stand still too long. Though I do like the concept. =3. I am seeing bunches of NV mods that I wish could be ported my way. I really don't want NV, I have my FO3 almost exactly how I want it xD. So, assuming that NPCs use stimpaks already, I suppose it's just an option of adding them to their inventory, or scripting or whatever you modders do that make you so awesome (I'm jealous =(). I'll give Arwen's mod a try, since I'm not running FWE, it sounds more compatible.
Arwens and FWE have similar goals with different ways of going about achieving them in my opinion. It'd be like the difference between making enemies harder with one mod increasing HP and another instead increasing their armor.
Not citing that as a specific example of the differences between them -- but that's pretty much how I view the two. That's the core of what Arwen tries to do -- just make the game more difficult and also more realistic. Aside from her Med-Tec module however, (which is vastly superior to Primary Needs included within FWE), I'd say they are both capable of accomplishing the same end result.
The difference being that FWE does many other things which Arwens mod does not, such as adding new weapons, armor, 3rd party mods such as sprint and bullet time.... Many of the FWE weapons are also iron-sight compatible if you search around... Both are pretty customizable as well although I can't say who has a more customizable version because I've only used Arwens tweaks for NV and merely read what her mod does on her nexus page. I prefer FWE because it seems to do more overall and there are more 3rd party mods that are specifically designed for compatibility with it through patches or just from the start.
I could go on but this is long already lol........ try both and decide for yourself.