You can knit them on larger needles and with the looser gauge, not so heavy.
To keep a stockinette (knit 1 row, purl 1 row) item from curling up on itself, you would knit about 5 sts at the beg and end of the purl row to form a border around it. Knitting the first 5 rows and 5 at the BO end will keep those ends from flipping up too.
Usually a scarf is about the same length as the wearer’s height, but guys usually like them a little shorter.