b) Would it be possible to issue some kind of credits/voucher system that automatically updates as per completed form? I suppose this will be possible

b) Would it be possible to issue some kind of credits/voucher system that automatically updates as per completed form? I suppose this will be possible outside the scope of Jotform

I think it will be possible to achieve outside the scope of jotform, you can also check out or widgets for inventory and gifts to see if they can fulfill your objectives.

http://widgets.jotform.com/widget/gift_registry

http://widgets.jotform.com/widget/inventory