Thanks for connecting with us here. I'll be happy to share more info so you're on the right track with achieving your QuickBooks goals. It's exciting to learn your client is looking to make the transition to QuickBooks.
When it comes to importing your data, QuickBooks allows you to import data from other apps such as Sage Business. I encourage you to check out the following article as it shows you how to: Import Data into QuickBooks Online. While there are import limitations with importing the inventory, you can also look into using third-party data migration apps that you can search for on our app store by visiting www.apps.com. I recommend choosing an app that suits your business needs based on the app description and the reviews.
Let me know if this info helps. I'll be one message away in case you have other questions. Otherwise, I wish you a great rest of the day.