I don't think I'd even think much about digging the usual footer trench without thinking really hard about renting a real trencher to do it with. Of course since you've got the kaboob and a bucket there's a certain uncertain satisfaction in doing the job with what you've got.
Unless the shed is going to be pretty elaborate, I'd likely have just used a grader blade - or the bucket - to level and take off some surface and poured a 4 or 5 inch slab; but again, that depends a little on the extent of the project, the geology, the bugs and boogers common in your area, and on building codes (if any).
(Our house is on a slab, and I can assert several disadvantages, hence the importance of yourher inentions about "nicieness" for the project.)