Does it make a difference which sector you visit?

Different areas feature different events, encounters and nodes.

• Nebulas will have approx 3+ nodes that are NOT sensor-disrupting nebulas.
• Homeworlds feature specific events that allow you to unlock some ships.
• Pirate sector got plenty of pirates (totally unpredictable)
• Race-controlled sectors will mostly have that race pilots (good luck boarding a Mantis crew of 5)

Although it's randomized, it doesn't take a load of thought to know what you'll find. Zoltan sector = loads of Zoltan = easy to teleport in and slay em. Rock sector = loads of stoners = teleport in, kite them around the ship, breaking their systems (they're too slow to ketchup)

TL;DR: Yes, there is a differense between regions, and red regions have more hostile encounters than green ones.

Yes. Sectors vary significantly in events.

The weight of different events can change (e.g. pirate zones contain almost exclusively pirate events) and some events are zone-specific (e.g. the Mantis stasis pod occurs only in Mantis zones).