No Spoilers, I promise!!
IMO, it isn’t necessary to watch 18 & 19 back to back if you’re feeling overwhelmed with the time constraints of recording in one sitting.
The finale, I would say yes (They aired on TV on 3 back-to-back days) But if you feel like you need to break up the episodes I don’t think that would be a big deal at all. Especially with the holidays upon us. Whatever works best for you though!