What's the proper ID type for cross-referencing data in Shopify integrations?

[wingra]

We're working on a Shopify tie in for our in-house inventory system. I want to make sure to get the ID types correct. From the documentation it says they are ID! types, with a string like gid://shopify/Product/[NUMBER]. I'm curious about the number portion of it. When looking at the documentation, it shows INT as -(2^31) to (2^31 - 1) which is a BIGINT in SQL or LONG in C#. I see there is also an UnsignedInt64 type that is 0 to (2^64 - 1).

If we are dealing with Orders, Shipments, Products, Variants, and Tracking Numbers, what is the appropriate type to use for IDs to cross reference data in Shopify?