give it some personal space.
No, if you treat them properly.
I don't think that is true. It's like saying a blonde is dumb, but they aren't. But female budgies are more aggressive than males.
Possibly if they are kept in the same cage and offered a nesting box, but usually budgies are monogamous.
It depends on the behavior of your budgies. If they are aggressive or like to stick around by the 2 mating budgies, I would suggest separate them because the female won't be comfortable with the distraction of the other 2 budgies. However, if the other 2 rarely come by the 2 mating budgies or completely ignore them, I suggest keep the two there.
There are too many variables to know what an "average" cage is. Part of it depends on the dimensions of the cage, part of it depends on the shape of the cage, and a lot of it depends on the budgies themselves. Females in particular can be territorial and aggressive.
This question is a matter of opinion. Some people like English budgies better than regular budgies or other people like regular budgies better than English budgies.
Imagine your head, look straight forward, but turn your left eye all the way right. You can see things 90° on the right side from your eye but not everything. Same thing for budgies they can only see a bit until they got to turn their head to see it.
Yes, budgies are parakeets.
Budgies are parakeets. They eat seed
Yes, they're called gay budgies, ey.
snakes eat budgies so you better watch out
Yes, budgies can certainly imitate whistling sounds.