What happens if you hit a limit? You can't add more prompts until you remove one or change your plan. You won't be charged extra unless you choose to upgrade.
A practical test before you pick: ask ChatGPT your three most important buying questions today, twice each, and note how often your brand appears. If the two answers differ, you've seen why one check isn't enough, and you'll have the start of your prompt list.
The common mistake when sizing a plan is tracking every keyword you already rank for. AI prompts work better as full questions, and fewer good prompts beat many generic ones. A freelancer with one brand and 12 buying questions fits Solo's 20 prompts. An agency with four clients and 20 prompts each needs 4 projects and 80 prompts, which fits Agency Lite, even if a bigger plan looks better value.