Deciding on a field type

In some scenarios it can be difficult to figure out which field type to use or for which scope to have the field in to be able to achieve the feature in mind. While there is not always a correct answer, some general principles may guide in the right direction for your scenarios
It can be very beneficial for you to make these considerations from the get go in order to make it easier for you to manage down the road, not having to change your setup later on.
If you have any doubts in how you should set up your intended use case, get in touch with us and we will be happy to assist you.
When adding a new field, ACF may restrict its field type to a specific selection. If you have a Shopify Metafield definition in place for the chosen name and namespace combination, this definition will determine your field's type for you, so the Shopify and ACF field definitions are aligned (as they should be)

Choosing the right scope

First off is to consider the data - would the same values reoccur across multiple objects? If so, utilizing one of the aggregate scopes may save you a lot of time and effort by allowing for one point of management of the data.
You can read more about the various scopes here.

Multiple selections or repeatable?

While the two settings can from time to time achieve the same result, it is also relevant to consider when it is right to use the one over the other.
Enabling multiple selections for a field is recommended if you need multiple values for just one field. If you have a group of fields that you need multiple values for, making the overall section of the fields repeatable would be the recommended way to go.
In general, we recommend not enabling any settings you won't need. It is much better to keep it simple and build your setup bit by bit once the needs presents themselves.