Satellites are defenseless and easily shot down, either one by one using ballistic missiles or by creating a sweeping ring of debris, in a full scale WW3 where things like treaties and sanctions don't matter
So you're sitting in your orbit and any changes (especially so close to the massive body) are super expensive. Which means sending anything after you must be pretty trivial (once the missile is already in orbit).
Spaceship just launched 30+ starlink v3 sats on its first orbital flight two days ago. It might as well have been flat disks of missile sats, even multi missile per each disk. Sitting there waiting, getting energy from solar, only having to expand fuel when a strong solar storm temporarily increases atmospheric drag on LEO + some minimal station keeping. A missile type sat with completely different budget for fuel and mass has a big advantage.
Maneuvering for a rendezvous (intercept), given 5-40 hours time, is very cheap in terms of ∆V (fuel used).
Only if you're in approximately the same orbital inclination. Plane change maneuvers once in LEO are very expensive in delta V.
Raising the apogee, then changing the inclination there is relatively cheap - and you can adjust the plane change and apogee to time a collision. Remember - there is no need to recircularize. Just collide. If the goal was to recircularize then I don't know if raising the apogee would be worth it, maybe for extreme cases. But not for a collision.