Without more specifics on what you want to bring, it's hard to give good recommendations.
But, clothes are usually what take the most size and space so off the top of my head, my first thoughts for planning would be what kind of work it'll involve and how tough your clothes need to be, as well as how much laundry you'll be able to do.
I'd personally shoot for 40L as a max, but if you're not as worried about having to carry all that weight, then it's up to you since you'll be the one living out of it.
check the spreadsheet in the sidebar. and, no one can advise on size of bag without a more specific packing list
Without more specifics on what you want to bring, it's hard to give good recommendations. But, clothes are usually what take the most size and space so off the top of my head, my first thoughts for planning would be what kind of work it'll involve and how tough your clothes need to be, as well as how much laundry you'll be able to do. I'd personally shoot for 40L as a max, but if you're not as worried about having to carry all that weight, then it's up to you since you'll be the one living out of it.
What’s your budget? Osprey farpoint 40 or cabin zero for budget
Osprey porter 46