Can I run 2 businesses on QuickBooks? I'm transferring from a sole trader to LTD company and the 2 overlap. Or do I wait till I wind down the sole trader account?

Welcome to the Community, @chris142. In QuickBooks, you can only use one QuickBooks Online subscription per business. 

In your case, I'd suggest you create a new company for your LTD business. That way, the transactions for each company are properly reported to the HMRC.

Visit this link to view the features and comparison for each version: QB for Small Business. You can also add multiple company subscriptions under the same credential. Refer to these help articles to learn more about it: 

• Create a new company and add subscriptions 
• Sign in to multiple QuickBooks Online companies with one user ID

Feel free to visit again if you have any questions in mind about QuickBooks. I'll be sure to get back to you and help more.