Not sure what you are asking here. I flew with a friend on the way over, and we took a bus to Gare Montparnasse, the train after that and arrived in SJPP in the early evening. The Pilgrim Office stayed open to process all of us who came in on the train. My friend and I walked to Roncesvalles the next day on Route Valcarlos and then on to Santiago.
At the end of my Camino, I visited my son in London, and then took the train to Paris and stayed a few days before flying back to Australia. My flight to London was on Ryanair. My wife booked this when it was clear when I would arrive in SDC. I booked the other transport once I was in London.
Paris was chosen because it was the cheapest option at the time. The return trip was booked through a travel agent. I have flown into other cities for different reasons on various pilgrimage walks, and organised to get from wherever I arrive to where I will start walking. I don't find this particularly complex or demanding. Unless there are some particularly complex connexions, neither my wife nor I would use a travel agent these days.
That said, it is clear from the questions that are raised here that many members seem to be concerned about organising their own travel. It is clearly an option to use an agent, and it might add to individual's comfort with the process doing that, even if I wouldn't do that myself any more. If anything, in my most recent experience using a travel agent they became more an encumbrance than anything else. Unfortunately, the flights were part of a rewards package with my credit card provider, and I wasn't able to avoid using their agency.