Always glad to please.
4. I haven't played MOO2 so I don't know how it works there, but in SE4 the mounts go for all direct fire weapons, ie beams and torps. Missiles and point defense are not affected by mounts. You can have weapons of different mountsize on the same ship if you want to, just change the mount before you put them on. Useful sometimes when you can't get anymore of the biggest mounts to fit but a smaller one will.
6. That's probably because of the fact the colonizable/breathable/empty routine still thinks the planet is empty but because of a small oversight by the programmers (or a minor bug) the little star dissapear when the planet is occupied even though you technically don't know it's occupied. I hope that makes sense.
As for seeing stuff in systems you don't have a presence, that's probably because someone you have a partnership with has a presence. You see all they see and vice versa.