Well, your first right step was
everything will be rewritten for the new system
because let's be honest, changing DRPG is a lot of work. The more you want to change stuff, the more you find yourself rewriting parts of it. (not trying to bash on DRPG, but it really was intended for an idea that's far different from yours (and mine))
And then you brought up some new ideas that could come from a rewrite:
-Improving weapons through actions
-Brick terrain
-Improving unique abilities acquired from an item
-Improving common abilities depending on your preferences
-Flags to mark territory
-Being a pirate
These are great first steps, now you just need to actually make this stuff work.