Importing in-store collection data to Klaviyo

My client is beginning to implement in store email collection for customers. They’d like to use the data to send them flows to nurture the relationship with the customer.

For context the brands sells wollen jumpers, mainly to American tourists visiting Europe.

When the customer makes a purchase they choose from three exclusive options. They will only be in one of these three paths

1. Ship the items home from the store for free. So they don’t have carry abound bulky jumpers for the rest of their travels. Their details are received from a third party and uploaded via a csv to klaviyo every couple of months
2. Get a tax back option when the go through customes. Details are collected immediately in-store via iPad sign up
3. Get a voucher for other store locations while on their travels - there are many store locations in the tourist areas of the country. Details are collected immediately in-store via iPad sign up

What is the best way to align the data collected in-store so that the flows can easily be created in Klaviyo?

Can we create columns in the csv files that will later become custom properties in Klaviyo? For example, demographics, items, purchased, location purchased etc.

Thanks a million!