Obviously spoilers ahead:
What you are supposed to do:
Ask around the novices background, think antonius is the most trustworthy, tell him about your search for pious.
Anonious is actually pious and will poison your food next time you eat.
Antonious is surprised you survived the poison, gives you and antidote and a plan to get out
You need goat blood and a key, go through the door at the end of the dining hall, there you are supposed to use a scroll, you are ordering blood you can pick up later.
Go a room further and you will see a key for every door on a shelf.
Go back to antonious to start some cutscenes.
Outside tell antonious you take him to the bailiff, fistfight and end of quest
you will not get his lucky die this way, you can continue the mainquest though without problems.
Sidequests in the monastery and the rewards:
Get a healing book, reward must have been shite because I dont remember it.
Find all the ripped out pages: Takes forever, they are quite evenly spread out so just find one per room, many in locked chests. Reward: Key for the bookshelf you need for previous quest.
Get wine, gets triggered if you spend a night in “jail” in the monastery, quest is quite easy when you have they key anyway, dont know reward, quest was buggy for me could not return whine.
What you can do if you want to skip the monstery:
Climb up the ladders outside the monastery and jump in (only read about this, dont ask me for exact spot)
Kill antonius/pious, loot die.
Lockpick your way out or pick up the key behind the dining hall.
I so far do not know if you can knock antonious out and carry him outside.
How to do the monks life:
Read the book about your daily routine
Be where you are supposed to be, remember you can wait and remember you can interupt waiting with escape.
Alchemy Job: Just brew the bloody potion, ingredients in a chest next to you, refills every day, brew away and raise alchemy skill. If you need lockpicks, potions are food and can be sold do get lockpicks.
Writing job: Just pick the latin phrase. Yes, this game was easy for me because I know latin, never thought it would come in handy. If you do not know latin I dont know how to do it. it doesnt matter anymway.
I spent about 2 gameweeks in the monastery, it is a great spot to boost reading, alchemy, lockpicking and pickpocketing skills. I dont like how learning to read is almost mandatory in this game, will do second playthrough as illiterate thief.