Is it possible to allow customers to attach a file to a sales order when they are checking out in SCA? I was having trouble setting a file on the liveorder model or to a custbody field, I'm wondering if this is just the wrong approach any help is appreciated!

Maybe create a Suitelet that will handle creating the file in the filecabinet with a POST request. have it respond back with the File id and then pass the file id to the custbody field.