The 360 degree weapons are the difficult ones. Even if you place the weapons hardpoint on top of the sphere, when it fires at a ship (or anything else) that is close into the planet, it will hit the shere. Might be ok for AMD, probably not Pl-D though.
In SFB, ground installations on planets had weird firing arcs and took atmosphere into account. For simplicity, if all the arcs are kept at 60 degrees, and shiplist weaponpoints match the model weaponpoints, with hardpoints on the outside of the sphere, that should cover most cases.
If you placed the 360 degree weapon point out in space somewhere above the sphere, that would help a little, and not look too bad. Needs some experimenting with though.
Damage textures on planets can be done. When the planet is captured, you record the damage percentage its taken and remove it from the map (silent destruction so no explosion). You immediately place a new planet in the same spot, exactly the same that has a model with damaged textures. You then reapply the recorded damage percentage to the planet. Requires special mission scripts though, and a new damaged planet in the shiplist and accompanying appropriately damaged planet model.
I might fire up 3D Studio Max when I get some time and try out moving the hardpoints.
Dizzy, do you still have that Tholian web model?