Agreed, but you can also put passives on the missiles and they will still target. Ships need active sensors to target, but missiles can find targets using only passive sensors. It could still be a good idea to use the same sensors on both devices.
I'm pretty sure they do need an active contact to hit, but you can still fire at a passive contact. Think of it this way, if you see a large thermal contact that is going really slow so you fire expecting you hit the motherload, and your missile passes strait through the center of the target. How can that happen, as it turns out it is really a multitude of ships flying in formation. However, if the missiles actually don't need an active contact, then I'll keep my missiles how they are for RP purposes, I like for the enemy to see their doom coming.
My fear would be that the missiles would only fire outside of that range. Are you sure it works the way you think?
Yes I am pretty sure as the separation range is described as the range from a target that a sub-munition will separate from the main munition.
Oh, and I think I found a kind of OP way to mine a JP if the mines really do stay forever (until target if found) and I can manipulate waypoints like you can with escorts. You put a few (5-10 I think) mines on the JP itself and have one or two every 30 degree offset at the ranges of 100k km and 250k km. Any other thoughts on how to use them?