Agree 👍 ALSA app is your friend, and in some situations can help you avoid unwanted passport/ID checks.
As mentioned above prepare to store all large luggage (anything larger than 25L, estimate) and follow usual best practices for keeping your luggage safe.
Online booking via MonBus
https://www.monbus.es/en/routes-points-of-sale/465/travel-fisterra-estacion-de-autobuses-santiago-de-compostela-estacion-de-autobuses/
1) La Estellesa bus ticket booking available 1 month in advance, via https://laestellesa.com/es/horarios-compra
Notes: Your name does not appear on the printed ticket. (see 4 below)
Two services 10am and 4:30pm; enter your travel date, starting point and destination for more...
This site is run by Ivar at in Santiago de Compostela.
This site participates in the Amazon Affiliate program, designed to provide a means for Ivar to earn fees by linking to Amazon