Certain number combinations could be not bad option, like website411.com or 123website.com But, I think it's much better to have a domain that start with numbers than to have numbers at the end. You can always have 1 or 1st and when you add your site to directories, your site will be the first in any category, and that will drive more traffic.
Nope, doesn't matter at all, even if your domain name is fitness12342314231.com it won't affect it, JUST MAKE SURE IT CONTAINS YOUR MAIN KEYWORDS (2MAX).
It depends in what way you mean. With regards to SEO i would say it wouldnt effect it, remembering the url?... quite possibly!
