Query on private Azure marketplace

Question

I tried implementing Azure private marketplace in our POC environment which is having almost 25 subscriptions. My basic requirement is I have to restrict all the services including third parties where users have to approach us to get approved their requests, Once we approved then can utilise the services in their accounts. So I was trying to figure out

1. How users can approach us, How can i setup a platform is there any existing API with MS or we have to setup any API where the customers can requests the services ?
2. What will happened if the user request is not approved on time ? can we setup any escalation matrix on it ?
3. How can we manage all the approved / Rejected / Pending requests in Marketplace services ? Can we setup notifications to outlook DL or Only to the individual emails ?

Any Help is much appreciated :)