I walked the Ingles in Holy Week in 2018, leaving Ferrol on the Tuesday of Holy Week arriving Santiago on Easter Saturday, a 5 day walk, allowing time to celebrate Easter Sunday in Santiago. If I had my time again, I would walk the Ingles in 6 days instead of 5, and break either the 1st stage into two (staying at Xubia or Neda), or better still, cutting the 2nd stage at Mino, and allowing time to enjoy the beach at Mino, which you do not see if you just walk through from Pontedeume to Betanzos. If I only had 5 days, I would substitute shorter earlier stages by walking from Hospital de Bruma all the way through to Santiago, missing out Sigueiro, as I found myself being able to walk longer stages later in the week, once I had overcome the doubt that I could walk 25 to 30km, or even further, every day.
Maybe because Easter fell at the end of March in 2018, instead of in the middle of April this, year, when I walked, I saw no more than 10 other pilgrims a day. Therefore, the Ingles was not busy at all.
I did not stay in albergueg (because I wanted a bath to soak my legs every evening and my own bed), but when I passed those to obtain a stamp, they had spaces. The albergue at Betanzos is larger than at Bruma. I started at about 08.30 each morning. It was pitch black in the morning before 08.30, and with the clocks going forward at the end of March 2019, I would expect that it would be pitch black until at least 09.15 in Holy Week this year. You do not sunrise to be so late, but it does mean that you have enough time to complete the long stages in daylight.
Where you do need to book accommodation is in Ferrol and Santiago. Ferrol does Semana Santa in a big way, with large processions every night. Betanzos also has processions, but on a much smaller scale. Expect many of the residents of Ferrol on the street each night, meaning that finding somewhere to eat is quite difficult, and it being quite noisy until late at night, especially at weekends. Also expect seaside towns such as Cabanas and Pontedeume only to have a handful of places open and look very much in off season mode. Santiago though was busy on Easter weekend.
But do not let that put you off a Holy week camino. I found walking through Holy Week as a kind of personal passion (but only a crumb of discomfort compared to the real Holy Week passion), and a real pilgrimage bringing me closer to God. Yes it rained every day (on one day it snowed), it was cold, the Ingles was very wet and muddy (take that into account in deciding footwear and how many clothes to take), but I was really happy that I walked a camino from start to finish throughout the Holy Week, rather than another week in the calendar.