Hi there! I can't answer all your questions. But, I have been to Gibraltar and a day is enough, unless you are a big history buff. The museum that goes over the Siege of Gibraltar. And, what role Gibraltar played in the American Revolution . . . fascinating! Also, you might want more time if you want to tour the caves and tunnels and see how Gibraltar was fortified. All historic sights, and all war related.
The main thing to do in Gibraltar is to take the cable car to the top of the rock and enjoy the view. You can do that and the main museum in a half a day, have a nice lunch, and walk around for a few hours the rest of the day and call it a day. Be sure to walk on the road that crosses the airport landing path, and cross the border between the UK and Spain. That is also cool to do.
By the way, there are a lot of monkeys and they are little rascals. They love stealing things. I lost a pair of sunglasses that got snatched right off my head by a baby monkey. He was too cute for me to get really mad at him. I hope he enjoyed my prescription sunglasses. So, when you go to the rock, make sure you have everything well secured, hats, and sunglasses. If you set anything down on the floor to take a picture, it's fair game to them.
Best of luck on your trip!