You'll be walking during one of the busiest weeks on the busiest sections so highly recommend that if you can delay your arrival in Sarria a few days, most of the crowd will be a few days ahead of you. Many schools and universities have the week off before Easter, along with everyday work folk and Camino is hugely popular for a 5 day walk. Sarria to Santiago will be very, very busy. Accommodations of any kind will be full and the trails, the bars, the restaurants will be packed. Since this is a late Easter this year, you'll probably have even more pilgrims then years past (with exception of holy years).
By delaying a few days you will avoid the biggest rush of local pilgrims who all want to be in Santiago on Easter day. Finding a place to stay in Santiago during Easter weekend may be almost impossible and really expensive (since Santiago for non walking pilgrims is also a popular Easter destination too). The good news is that many of the private albergues start opening in anticipation of Easter, so more beds will be available. A good way to check how busy places are is to hop onto Booking.com and check vacancies and prices at hostels, hotels etc. on various dates at major evening stopping points from Sarria. You may find that a couple days after April 16th from Sarria, accomodations start to clear along the way.