A few decidedly newbie-ish questions

[Taz-in-Space]

Satellites are also good for warp point defence.
Their advantages: they can be built on any planet
they use no maintance
they can be picked up again and reused

[capnq]

The most common thing that upsets an AI is seeing that you've colonized a world that they could, especially in a system they've claimed (see [F9] Empires/Borders).

However, the Mood listing doesn't reliably correlate to your current treaty status; "Murderous" allies and "Brotherly" enemies appear fairly regularly.