The 1 or 3 companies really depends upon how you're set up. If you did create 3 different business entities (LLC, Sub-S, etc.), then you will need 3 QB online accounts to keep the business books separate. OR, you can buy QB Desktop and open as many companies as you want. They're just separate Company Files on your computer that you open in QB Desktop.
If you really only have one company for Tax purposes, then under Income, you can set up three Sub Accounts for Writing, E-Commerce and Uber. You can also use Classes to keep the Expenses separate too, but I don't know if you'd need to go through the hassle. You should have a quick conversation with your Tax Accountant and they get give you direction on how they want to see the books at the end of the year. Three separate sets for legal reasons (so 3x QB Online Accts), or just one QB Acct since it really is just one entity.
