I just ordered myself a new P3 and was wondering if it is going to arrive with the latest firmware already installed or will I have to download it?...thx

That's completely dependent on when the Phantom was manufactured and packaged up.  Most likely you will need to upgrade the firmware, but if you are lucky and get one that was manufactured and packaged in the last couple weeks, then you'll have the latest firmware installed.

Most likely not.

Just got a 2nd Advance as  a standby from DJI on Friday and it had the 1.2.6+ firmware on the RC......had to update both the Phantom and the RC.
I would say highly unlikely.

Just received a brand new Professional and it came with 1.19 on it.