To connect 2 computers together to share files i would use ethernet cables.
Willott I am afraid i was unable to even attempt your first question.
If you are setting up a network in your house it depends on the size of the house, if you live in a small flat or small house wireless should be strong enough to reach all corners of the house with a decent speed. However if have a much larger house a wireless signal from a single modem would struggle to reach areas of the house, therefore in that case i would go for wired.
If you are setting up a computer suite of 30 for media editting i would go for wired, because the amount data from media such as film is very large therefore i think you need the speed of wired to keep it quick enough.
I hope i got the right idea of the questions, please do correct them as i think it would be of great benefit to me.
Thanks Jimmih