When should a small business stop using spreadsheets?
When the file has stopped being something you think in and turned into something you maintain. The signs are easy to spot: more than two people type into it, somebody rebuilds the same summary by hand every week, there are copies called final and use-this-one, a mistake made on Monday surfaces on Friday, and you cannot hand it to the person who needs it because it also shows what things cost you. Any two of those and it is time. What you move to does not have to be a project — send PaprPlain the same file and it builds the workspace out of it for you, and you keep the spreadsheet for the thing it is genuinely best at, which is working a number out.
Moving is not a project
Send the file. Check what it built. Invite your team. Start with the list that hurts most. The comparison.