Hello Mir,
1. You want to setup Elastic for SAAS model or you want each customer separate delivery server or their own delivery server ?
2. To use Elastic email, you just need to use API option, so bounce/complain all will be managed by API.
3. You can set in Customer Group - Domain must be validated or in Delivery server also, so without domain verification they cant send any campaign.
Hope it helps.
Thanks,
VPul.