How to cook for a big group I have to prepare a meal for a group of 60 people. I already have a recipe (Japanese curry with rice) but I have no clue how many of all the ingredients I need, because when I cook it for myself I just put things in the pan without measuring anything. 

So that brings me to my question:
How many ingredients do I need (in total or pp)?

The things I use in the recipe are:
- Japanese rice (separate)
- potatoes
- sweet potatoes
- big carrots
- onions

I was thinking about 100 grams of (uncooked) rice per person, so 6 kilos in total, but I have no clue how many of the other ingredients I need in the curry itself, or what amount is normal for veggies in a meal.

I will serve sausages with the meal, but separate because of the vegetarians who are attending.
If you have time, make the dish at your normal size and measure everything you put in. This will allow you to get a recipe with proportions that you can use for your full party. Measuring weight is best if you have a scale, but volume should still be significantly better than guessing. 

Say you make your dish and it uses


w grams potatoes 
x grams sweet potatoes
y grams carrots 
z grams onions


If this feeds 4 normal people, then for 60 people you need


(60 / 4) * w grams potatoes 
(60 / 4) * x grams sweet potatoes
(60 / 4) * y grams carrots 
(60 / 4) * z grams onions