Any cake makers about? I need icing help!

[Fullofpudding]

I need to make 50 cupcakes with rainbow swirl icing. Could someone help me with amounts. I'm a confident home baker but have never iced using multiple coloured icing before and if I run out I normally just make some more which I don't want to have to do with the multiple colours. How much icing sugar would I need? Thanks.

I would brobably go with about 1.5kg and 3 packets of butter (and a big glug of banilla essence) but thats big high swirls like a 99 ice cream. Im not great at measuring either to be honest even though i did dozens on sunday.

*vanilla- obviously

I'd probably go a bit more - I'd probably mix 2kg icing sugar, and about 700g of margarine (dairy free here so 50/50 mix of stork block and pure spread). The fat varies a bit, closer to 1:4 fat:sugar when it's hot but that's a personal preference.