I sow first and net, but only about 6" off the ground. I use debris netting at this stage, well weighted down to keep the mice off.
I don't faff about with chitting them, transplanting them or starting off in guttering etc. (the quantity would make that impossible), they are just thrown into a shallow trench and left to get on with it. Remember - for each foot in a row of peas, you need at least 15 peas. I grow 36' rows - at least 4 of them and that equates to 2160 plants - I'm not faffing with that quantity!
Only when the peas are a few inches high do the supports and twine appear, the debris netting then moves on to be used elsewhere for brassicas and the like and it's replaced with any old netting sufficient to keep the pigeons off.
First stage:
Photo 1
Then increase the levels of the twine until you get:
Photo 2
and then:
Photo 3
and
Photo 4