I wouldnt stress anyways cause legacy goes up rather fast. I have one level 50 and a level 45 and im already legacy rank 13 or 14. And as mentionnend, all xp gathered once you are 50 will still give its % to legacy, so you never stop making it. The only thing that could affect you tho is if they eventually add bonus starting features like looks or races ( if we are very lucky) with the legacy points, but this is only a problem if you already have a zillion alts. But even with that, worst case scenario is you re-roll one or 2 of them some day. level 20 is pretty fast to get.