Most people I know who have gimbals say don't fly looking through the camera on the gimbal as it stays level and it's hard/impossible to know what the attitude is when you're looking through your Fat Sharks/monitor. If you're going ot do FPV I highly recommend using a flight cam hard mounted to the quad body.
Also have fun, the Phantom is a great beginner quadyou'll get addicted in no time and then want to build your own faster quad
I love blasting around in mine flying FPV.
Edit: Oh and balance your new props, you'll massively cut down the vibrations that cause jello (the wobbly looking video caused by the camera moving during an exposure) and give your flight controller an easier job.
Edit2: also get some circular polarised antennas for your video transmitter (VTx) and goggles/receiver, you mentioned a 600mW VTx so I guess you've gone for ImmersionRC, good choice, I'm on their frequencies too, you'll need make sure you get SMA connectors on the antennas (rather than RP-SMA). They will increase the range you can fly and eliminate the multipath interference you get with the standard rubber ducks.
I have a small cam for FoV for exactly the reason you say.
Have balanced the props.
I have circular polarised antennas too

I'm not new to flying. I have a Trex 450.
I was going to build an F550 but I figured that the Phantom would suit my needs and be more portable.