Reseller, master reseller and alpha reseller are sold as if they were small, medium and large. They are not. The disk and bandwidth differences are incidental — what actually separates them is who you are permitted to create underneath you.
The one distinction that matters
Reseller. You get WHM and can create cPanel accounts for your clients. That is the whole scope. Each client gets a normal hosting account; you handle their billing and first-line support.
Master reseller. Everything above, plus you can create resellers — each with their own WHM, their own allocation, and their own clients you never see.
Alpha reseller. Everything above, plus you can create master resellers. Three levels beneath you.
So the question is not "how much space do I need". It is "am I selling to end users, or to people who will themselves sell hosting?"
Choosing honestly
If you build websites and want to host the sites you build, you want a plain reseller plan. Almost everyone in this position over-buys. Twenty client sites on shared hosting rarely need more than 25–50 GB, and if a client outgrows that they should be on their own plan anyway.
If you have people selling on your behalf — a friend in another district taking local clients, a partner agency wanting their own panel — you want master. The moment you find yourself creating cPanel accounts and then handing over the login so someone else can manage them, you have outgrown a plain reseller plan.
Alpha is for building a network rather than a client list. It is genuinely useful if that is your model and pure overhead if it is not.
Overselling, and what it means
Reseller plans usually allow overselling: you can sell 50 accounts of 10 GB each on a 100 GB allocation, because most accounts never use their quota. This is normal and how the industry works.
It is also how resellers get into trouble. Overselling is a bet on average usage. Land three genuinely heavy clients at once and you will hit the wall with no warning — and it is your clients who feel it. Keep some headroom, and watch actual disk use rather than the number of accounts.
The part nobody mentions
Reselling is not passive income. You are taking on first-line support: password resets at eleven at night, email deliverability questions, "my site is down" messages that turn out to be the client's own plugin. The infrastructure is the easy part.
Start on the smallest tier that fits your model. Upgrading is a few minutes of work; discovering you bought three tiers more than you needed is money you will not get back.
Our reseller plans start at 25 GB with 5 cPanel accounts, and every tier includes free WHM, free SSL and overselling. Move up whenever you outgrow it — we prorate the difference.