since you already have something set up and you seem to know the basics of a reseller account, not sure what more we can tell you since you don't want to offer to the general public. Just make sure you give them hard limits and keep an eye on your space and bandwidth usage - it can get tough to track if you're on a reseller account and you aren't used to checking your resource usage (I am the same with my private servers).
You can start with entry level package and offering small volume to your client. but, normally entry plan didn't come with some free stuff like billing, private label...and so. you need to consider abt this.
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