Cross sell email with free shipping on specific products

[Joshhy2100]

I'm creating a post-purchase email campaign and using Klaviyo.
The first email I want is if they want to add any smaller products to the previous order before it ships, without paying another shipping rate and preferably without adding another discount code.

I have noticed that in Shopify under "Customers" you can create groups and then add discounts to that type of group?
How would I create a group to automatically add customers and charge no shipping?

The rules would be if they have purchased in the last 4 hours and to specific products only.

Then once the 4 hours is up their discount expires automatically. Meaning they can't order 4 days later once their original product has shipped. 

I also have another email to a different group with the same principle of adding extra small products to the order but including a 20% discount code and free shipping. Is this also possible?
Thanks.