Plans
Which plan size to start with
Start from the number of sites and databases, not from the word unlimited. You can move up later and pay the difference for the remaining term.
Count sites first. One site is Basic. Two to ten is Professional. More than ten, or a pile of databases, is Unlimited. Disk is the second count: 70 GB, 150 GB or 300 GB. Mailboxes follow the same ladder: 10, 20, or uncapped.
Do not buy Unlimited for CPU. The CPU cap does not move. A busy WooCommerce catalogue that needs a resident worker will feel the 1 GB RAM limit on every shared plan. That is the moment for a VPS, not a bigger shared label.
You can upgrade mid-term and pay the difference. Downgrades wait for renewal so a site is not deleted to fit a smaller disk.