I was nervous as anything when I arrived in Ferrol on the same afternoon train, albeit on a Monday, as opposed to your Sunday. The following helped calm me down.
1. Walked to the hotel via the Praza de Espana tourist office (waited 5 minutes or so for it to open). Obtained a good free map of Ferrol which usefully had my hotel on it, and also a marked route of the Camino Ingles through the town, as I had read that some people had become lost following the Ingles on the streets of Ferrol.
2. Checked in at my hotel and dumped my stuff.
3. Walked down to the harbour to the find the start of the Ingles. Obtained a my first sello at the tourist office by the harbour (they automatically dated it on that day, but I could have asked for the stamp to be dated the next day, if I wished, as the date is handwritten, and if I had my time again, I would ask for this).
4. Using the map given by the tourist office, walked the first 2 kilometres of the Ingles through the streets of Ferrol (via the Cathedral) until the old town stopped.
5. Walked up to the tourist office at Praza de Espana to obtain a second stamp (with the same date stamp as the first).
6. Walked back to explore the old town and popped into the large supermarket in El Corte Ingles (calle Dolores- open till 9pm) to stock up on fruit, water and other provisions that I would need for the next day or so, noting that, like the tourist office, shops only open too late at 10am in the mornings.
7. Prepared my pack at the hotel for the next day.
8. Went for something to eat. One of the quirks of Galicia is that whilst I wanted to eat something early when I arrived and then turn in for an early night ready for the next morning, unless you go to McDonalds, you basically cannot find anywhere to eat until 8pm. The above gainfully passed my time until then.
9. In the morning, at the hotel, made myself a packed lunch from the breakfast buffet, and obtained a stamp dated that morning from the hotel.
What all the above meant was that on the first morning, I was able to walk straight out of the hotel and down onto the Camino where it was nearest to join. This saved me 30 minutes or so of walking, because the stage to Pontedeume was long.
I also had my stamps at Ferrol which gave me great peace of mind (in retrospect, I would have asked for all stamps to be on the day I started walking).
With my packed lunch and supplies purchased from the day before, I had supplies to last me through the day, in the event that I could not find lunch, or I simply arrived at places the wrong side of lunch (another quirk of Galicia - places generally serve lunch only in a certain window).
Doing the above stopped me from being (too much) of a nervous wreck as I walked out the hotel door on my first Camino day.