Invoice Data Structure

Hello Bubblers,
I need assistance on the best way that i could structure my invoice items data type properly.
My app creates invoices for tour company in Tanzania so far i have been able to collect data correctly.
I have following Data Type
National Park Entry Fees
Activities Fees that are done in the given national park
Accommodation within the given national park
So in my Invoice Data Type
National Park Entry Invoice item
Activities Invoice item
Accommodation Invoice Item
So far
I did have i look to some of other invoice system data structure like stripe which was interesting i can say like for invoice item
It has the following field
1.ID (i think it is like bubble Unique ID maybe)
5.Meta data (set of key value pairs . This can be useful for storing additional information about the object in a structured format. Note that for line items with type=subscription this will reflect the metadata of the subscription that caused the line item to be created.)
6.Price (which interesting thing it had its on DB )
7.Period( which its created field in bubble)
9. Proration

What can you advice me the best possible solution field that i must have ?