A lot of that would depend on how you want to stock it and how densely planted you want it to be. For me, the way I know there are enough plants is when I run out of substrate.
For 25 inches of height, I'd definitely use some swords - I think the leaves would look nice twining through the branches of your driftwood. They are very easy for me to grow. Just make sure you give them root tabs, as they are heavy feeders. One of my favorite swords is ozelot sword, but I don't think you can go wrong with the old standby Amazon sword. Vals get tall also, jungle vals and contortion vals might be something you'd want to consider.
Then, taper your plant height shorter toward the front. If you are going to want color, keep that in mind with the mature height and spread of plants at the back of the tank.