1) Sling has a ring; pouch has just an opening. Only a sling requires you to adjust.
2) Yes, both are draped across the body.
4) MIM carries both pouch and ring sling; Pupsik sells only pouches.
5) Anywhere really - Mothercare, MIM showroom/website, Pupsik website, etc.
Below is a pic of me using both MIM ring sling (left) and Pupsik pouch (right). I prefer the pouch for now because it's easier for me to "dump" her in whereas with the sling, I have to adjust fabric and such. BUT in terms of security, the sling is way better - no big openings. It's a personal preference, IMHO.