If you have a preorder code, use it on the PS3. That way you can play early on the PS3.
The P4 invite you got for being 1.0 is the same client, if you used that and played in P4, update it and you will be able to get into the early access on your PC. The only way to get the PS3 client download is by using early access on the PS3 or have been invited to play in P3 (I think), or had been invited to play on the PS3 in P4. Otherwise you need to use the code to be able to DL it.
Everyone from 1.0 was automatically in P4 so you should have got the client.
Then so answer your real question... Provided you have both clients downloaded, yes, you can play early access on both. The PS3 and PC are both connected to the same server, cross-platform play, and this makes your character usable on both platforms. Since your account is accessible to both systems on the same server.
The only other thing is that you have to LINK your PSN to your SE account. When you start up the PS3 you will be prompted to link them.
I hope that helps.