Thank you everyone for all of the replies! Peggy - I came across that tutorial in my research, that's definitely the approach I will be taking with these, but I plan to make smaller ones, maybe slightly larger than a crib size? Something to cover up with on the couch. I'd love to make bigger ones but I'd have to use a lot of purchased fabric then (I don't think I want to add thrifted sweaters to my Dad's, I feel like it should be only his stuff and purchased stuff)
I will have to check through all of my Dad's sweaters, but when discussing with my mom, she believes that most, if not all of his sweaters have a decent wool percentage. I do plan on felting them before cutting them, which would solve the fraying/unraveling problem, and then it could also be washed at home right?
As far as climate, I live in Alberta, Canada, so I am not worried about it being too warm or thick!! I really, really want to try use both shirts and sweaters for the squares, so I will have to do some more research on that!
I have found some nice wool fabric on etsy that might work for additional squares also.
Thanks again everyone!
ETA: I think making a "practice" quilt from thrift store finds will be happening very soon!