Yes - Only .US domains have a restriction to either own a business in US, be a resident or a legal presence.
Yes, anyone can register a .co.uk domain. One point you might want to be aware of is that UK domains get registered two years at a time for some reason, so if you see a price advertised at X per year, you'll likely need to pay twice that.
Well if your preferred .com or .net domain is registered then you can register your .co.uk domain. It's also good if you have a business geared towards the UK audience.
Excellent for sites that focus on the UK market. You'd also see that you can rank fairly easily .co.uk's and .org.uk's in google.co.uk As for registrars for .co.uk domains, I'd suggest either 123-reg, Daily or some other similar registrar. At around £3 for two years, .co.uk domains are cheaper than .com's.
godaddy.com? the only one thing - you cannot input any data as owner for domain name. and you cannot change it from godaddy panel.