Hello,

The basic idea is that just like "Item Limits" admin can set "EMAIL LIMITS" ie. based on a payment plan the advertiser purchases, like 20 email inquiries or 50 email inquiries, etc., but there should be a override so that the end user can also pay for a plan for the amount of emails they want to send but as long as one party is paying then they can send or receive set amount of emails.

This will not only allow extra income but will also cut down on SPAMMERS who send hundreds of emails every day to advertisers. If you are going to do this (I hope you will) then also consider email lead logging/tracking in the account panel for the end user ie. the email sender/date/ etc., will be logged so they can see a log, and the admin can set how may inquiries can be stored by default say (25) and then older inquires get purged by cron, etc.,

Ok so you basically means to make contact form to be paid.

Whether it is going to be paid or not should be up to the admin to decide - in fact, for starter and new sites admin can keep it free and not charge but later when there are more users, admin can create payment plans or make it pay-per-lead so the user signs up for a paid plan or pays-per-lead from the wallet? The basic idea is to set email limits per user or per plan.  Like I mentioned, just as in the item limits plugin, the admin can enable, disable, OVERRIDE settings/limit for individual user, etc., and either keep it free or paid. 

Also, please make it so that it will work with any payment plugin like the original osclass free paypal plugin and wallet - so the plugin can send the payment by hook or something to any other payment plugin.

It should also able to keep track of the number leads sent, etc., and keep email log, etc. for which admin can set limits. If you are going to make it please reply and provide an update when you start the project - I will give some more suggestions - I had thought about this a long ago and don't remember all the features I was thinking of. Thanks.

I see, unfortunately it is not feature worth to develop right now.
There are more important topics to do now, anyway will keep it on the list