http://www.butkus.org/chinon/dacora/...cora_digna.htm
this might help. Normally with 120 film you wind it all the way onto the second spool, unlike 35mm where it has to be rewound. I usually wrap it in tinfoil for good measure but in theory the backing paper is lightproof and the spool ends prevent light getting in the edges. You then swap the now-empty spool to the other side for the next film.
Where are you getting it done? I've been using these guys:
http://www.peak-imaging.com/htmls/pr...tive_film.html
also what size do you get for that? 5x5 is not far off a contact print, but Peak Imaging will store scans of MF negatives so you can order enlargements without sending the film back. 8x8 is roughly the same as a 6x4 off 35mm in terms of the increase in scale so you would expect no problem going that big if you get a good picture.