I surfed Huntington in late November with no problem in a 3/2 and I'm quite susceptible to the cold, to give you an idea.

Probably err on the safe side with the 6'3. I was surfing 4-6' Huntington quite comfortably on a 6'1 CI Flyer.

Don't have enough experience to inform about the rest.

I've been over there in December/Jan - obviously a bit colder- but from county line down I was good in a 3/2.
What's your travel range north to south?
I scored great waves from Santa Cruz all the way down to San Diego.
The lineups are busy but if you're assertive you'll still get waves.
Rincon when it's on is pretty awesome, but a battle to get a good one. A board with a bit of volume helps battle the longboarders and the rippers!
I opted for Uppers over Lowers - as a reference there were around 20 guys out at Lowers and 5 at Uppers the day I surfed there.
Unless the forecast is really good it's not THAT crowded - (much easier to get waves than Trigg Point!)
There are a lot good waves aside from the name breaks from Ventura down to LA and beyond.

If you wanna chase the points you'd have heaps of fun on the twinnie.

Awesome. Thanks Mick. I don't have much time over there as the family want to do other things so I'll squeeze a few surfs in between Disney Land, Hollywood etc. I'd rather spend most of my time on the coast between Huntington and Trestles, but really want to surf Rincon so will make a quick trip up there just to do that.