I'd like to make au gratin potatoes in the crock pot.

My mom has always bought the boxed kind, so this is my first time doing
it from scratch. I've looked at several recipes online, and they all
say shredded american or cheese soup. Would shredded cheddar melt okay
in it? Would it be too greasy?

The recipes I have say 1/2 can of cream of mushroom soup. Which size
can are they are using?