If you want to play on either the PS3 or PS4 for 1 person then you would have to buy a copy for each platform, so if you also wanted an account for your wife and the ability for her to play on either console you would have to buy a total of 4 games (2 PS3 and 2 PS4 copies).

Currently PS3 gamers can upgrade to a free copy of FFXIV on the PS4 (at launch) but once you transfer you can no longer log into your account on the PS3, hence why you would have to buy a copy for both platforms per person to be able to play on either one.

Your subscription time is linked to your account, so if you have 60 days on your account that covers play on any of the platforms but like I said above each platform you want to play on much have had a registration code used. So to clarify if you wanted to play 1 account on the PC, PS3 and PS4 then you would have had to buy 3 copies of the game (1 for each platform) and registered them against you SE account.