The distance limit for your destination alternate would be the distance your fuel on board would allow you to go. I think for an alternate, as long as it comes within weather minima requirements as the alternate, u can use it. Normally, if u are required to plan an alternate, u wouldn't really want to plan the alternate aerodrome which is furthest away, u would want the closest one which would allow u to land if your initial aerodrome's minima came to the point that you needed to divert. As long as your alternate aerodrome came within alternate restrictions (Say, Night VFR Alternate requirements etc....) but that's a different story..... =)