Google Accounts & Mail Merge

I purchased the premium version of Mail Merge. I run several different accounts through Google. It appears that the premium version got attached to my personal Gmail account and I cannot attach to my google contacts in the business account.

How does all of this work? I need to be able to use this attached to the business account for setting it up and then transfer this to 3 or 4 other users in the office.

Do each of them need to have this attached to their Google accounts run through my Google app admin account?

You have mentioned that the 100 a day limit will grow after a billing cycle or so. Do you know how long this takes?

Please advise.