I heard that we need to buy an app for $4.99/year called pokemon bank to transfer stuff. Last time i played two pokemon games in a row i got bored and never finished the second. So, i might just play x/y then.
Personally, I'm waiting to finish X and Y before I revisit fifth gen (from which I've only played Black 1). Once I figure out exactly how many Pokemon I can get out of X and Y, I'll map out which games will be necessary to complete the Dex.