They're generally known to be defensive, more or less.
If you get a US captive bred animal, it'll probably be more docile than the cheaper wild-caught imports. But that's not saying docile like a ball python or boa LOL.
There are different locales of WLP, so the answers to your questions will depend on locality.
Southerns will typically be in the 8-10 foot range while D'Albertis will typically stay closer to 6-7 feet.
These are the more common two in the pet trade.
As for temperament I've read varied responses but they are known to be a bit nippy and challenging to handle. The captive bred animals are usually much more calm than wild caught.
Hey there! Just wanted to chime in and say that I have a CB female Northern white-lipped python and she's super chill. I have a recent video of her here: https://youtu.be/_p_DInFPXY4
I highly recommend purchasing a CB individual. You will pay more, but not only will you get a calmer animal, you will be supporting breeders who are working hard to make a strong captive population of this species.