Secondly, I was thinking about making a new domain "sneakersonline.co.uk"(just an example) and redirecting the first domain to this one. However, the first domain is already ranking well in Google and I don't want to lose it. Is it possible to 301 redirect the first domain to the second, but not make the first domain visible in Google, but the second. So you'd see in Google "sneakersonline.co.uk" when someone searches for "Adidas sneakers" but in reality it's just a 301. I've heard some people did that.
I'd appreciate your guys' input!