Good day, @Tidler.

Welcome to the QuickBooks Community.

Right now, there isn't an option to automatically enable attachments on the invoice in QuickBooks Online.  In the meantime, you'll need to manually upload the attachments to each invoice. 

Having this option to apply updates, such as customer address, to future or existing transactions is a great idea to add in our program.

Our developers have a massive product roadmap. They are implementing new features based on the functionality that works best for most users. 

For now, you can visit our QuickBooks blog site so you'll be able to the latest updates and features in QuickBooks Online.

To know more about the online payments limit, please check out this article for future reference: Online Payments and Processing Limits.

If you need anything else, please post a comment in reply button below. Helping you will always be my pleasure. Wishing you and your business continued success.