Managing dozens of domains as a reseller.

Edit Subject

I'm looking at becoming a reseller of Sendgrid.

I will likely have several dozen or more domains to manage.

So I'm trying to figure out the cost structure for handling this.

The actually volume on a per domain basis will be low.

My question is what package do I need, and what is the cost for managing those domains.

Is getting the silver or gold plan and sharing the IP for whitelisting amongst all the domains sufficient?

Thanks.