It's insane to combine the three ED movies into one, it's just not possible due to cast and plot changes and you wind up missing out on some of the best parts of all three movies (which are the recaps and how they change or suddenly include Bridget Fonda).

Better to do the films separately.

Extending and fixing Army of Darkness on its own is definitely a good idea.

I actually did this myself a few years ago on digital8. Some ED2 shots were used at the beginning, Sci-fi and other deleted scenes inserted, etc. Would like to see AOD properly restored using the actual M2V encode from the MGM version as much as possible. Dig it.