PS3 doesn't really matter at this point anymore since it being discontinued in about 2 months, and going to be forced into PS4 only then. Also unless you talking about like your hotbar setting there no character data transfer as that all resides on SE servers so no matter what system you play on you will have access to same characters regardless of system logging in on.

Until June, if you have bought both PS3 and PS4 copies then yes you can log onto either one if you used the free license transfer then you will only be able to use the PS4 version.