Glad to see you here in the Community, @jeanh352.
In QuickBooks Online (QBO), there's no limit to the number of transactions that can be posted to an account.
I've added this link on how to account items for product/service: How to change the account for a product/service item.
Also, you may check this article about setting up and use products and services list: How to create and use a products and services list.
Don't hesitate to reach back out to me if I can be of additional assistance. I'll be around to help you out. Take care!