Estimate mocktails per guest.
Drinks planning works from a rate, not a total: guests times drinks per guest per hour times the length of the event. That rate is higher for non-alcoholic drinks than for alcoholic ones — people drink soft drinks faster and with less self-limiting, so around 1.2 an hour is a safer planning figure than the one drink an hour often used for wine. Converting to volume and then rounding up to whole bottles is what turns the count into a shopping list.
Drink count
Mocktails = ceiling(guests x drinks per guest per hour x event hours)
Shopping
Volume = drinks x serving ml; bottles = ceiling(volume / bottle size)
Generally yes. Without alcohol there is no self-limiting effect and the drinks are often lighter and more refreshing, so planning at the same rate as alcoholic drinks tends to run short in the second hour.
Batch everything except the fizz and the ice. Mix the juice, syrup and infusion base ahead, then top with sparkling water at the point of serving so it does not go flat.