unit status meters
Yes that's a good idea. One of my design principles is to make the simulation as transparent as possible. No secret recipes or hidden variables. Players should be able understand the state of a battle from a quick glance, and apply sound tactical principles in order to win. If something is hidden, it's because the simulation rules explicitly says so (line-of-sight, fog-of-war, etc).
buildings and sieges
Fortifications are powerful immobile weapon systems, and sieges being asymmetrical are very different from the current meeting engagement type of battles. Need some thought on how to maintain balance and make them fun.