Generate automatically incremented check numbers for "Generate Check Payments" process

Experts,

Request your help here.

1. Can we add custom parameters in a flow pattern copied from "Generate Check Payments"?
2. We need to retrieve the last generated check number for each payment source (Like Check , payment to third party etc) , increment it by 1 & display it on screen whenever someone tries to submit the process.
3. Can you share a sample query for this?

Any pointers around this problem will be greatly appreciated.

Thanks,

Aloka