You can use the same Service Account to login, to have PS4 beta license attached. The characters created during Beta phase 1 will not be carried forward to Beta phase 2 and release. The Beta phase 1 server is situated in Japan and will be wiped at the end of the phase.

You need to have PS3 copy to be eligible for PS4 beta (I think, I may be wrong here). However you do need either PS3 copy and upgrade it to PS4 when the game is released - effectively void your PS3 license. Or the recommended step to play on PS4 is to purchase the PS4 license, and keep the PS3 license for use on PS3 - if you want to play on both PS3 and PS4 at different time.