Re Pricing - I'd be interested in being able to buy a number of "credits" for this service instead of paying a recurring monthly fee. Something like $20 for 500 requests that I can then use anytime over the next 12 months.

Your service looks interesting but also something I'm likely to use a lot for a few days then possibly not at all for a while so I'd be reluctant to pay a monthly fee for it. A "credit pack" or pay-per-use ability would be a great alternative