Is my plan a good idea?

[Saint]

That's not quite what I meant, though that is one approach. I imagine this doesn't scale very well though, and that's likely why most "hash cracking websites" limit you to 10-15 hashes.

I don't see why so many hash cracking websites are so bad though. The success rate is very minimal, the best free one is probably hashes.org, and they only use their own wordlist which is 2.5GB.

If lots of good hash crackers kipped together and shared their wordlists they could make one hell of a good site and make a bit of cash out of it.