This is exactly where I got my start in modding OFP back in the day.
I'd really like an element of a mod, like the weapon models or a new feature, but I'd hate the way they had modeled recoil, or weapon damage, etc.
You're going to need to download a PBO packing and unpacking utility, an "unBin" utility, a good coding program like Microsoft Visual C++ is an excellent help because of it's color coding and ability to search all the files in a directory for a specific phrase (although you can get by with Wordpad), whatever modeling program is used for Arma (it was oxygen for OFP), whatever texture converter is used for Arma, and then learn how to use them all.
Pulling just the weapons and soldier models out for use in the game isn't that hard. Easiest way would be to write a simple mod of your own (if you can find a simple weapon addon mod that also comes with a new soldier, I'd look at that and use it as a template). Basically, you'd need to put the ACE mod's PBOs in your addon directory, write your own mod that references the models and/or also the weapon mechanics they wrote (or you could use your own weapon settings), and then pbo it and run it.