Yes, you can move in the future. And if you set up redirects for all pages, then Google etc follow those and use the new URLs.
But ideally, you should pick one model (www / no-www), and keep it. If you switch and you don't get the redirects right, or have the wrong setting in Google Webmaster Tools, then you can dilute your inbound link count. That would be bad for your search engine ranking. Additionally, if users bookmark the 'old' URL and you redirect them, then there is a (very small) performance penalty. So I would recommend picking either www or no-www and stick with it.
"www" / no-www is a topic developers have strong opinions about (and often fairly bogus arguments for / against). I have not met any typical users who cared greatly about this. My personal preference is with "www", as I think works best in brochures and other marketing materials. But no-www is also fine; they both work fine as long as you're consistent, and you redirect from the one you're not using to your preferred one.
Edit: Here is a good discussion on Stack Overflow about www / no-www, with links to good articles for both viewpoints.