ISO: making neeps and tatties for 100-Scottish help needed

HI, I've been asked to make the neeps and tatties for our Burns Night supper in January. They're buying the haggis from a place in New Jersey, and the rest of the evening is catered, so I don't have to worry about that.

Now what would be a good recipe to use for the neeps and tatties? tatties, just mash and put in a LARGE roasting pan? And approximately how many pound should I make? Anything else good to put in them, sour cream, onions?

I've had some conflicting advice. One lady said sour cream and onions are good, nothing green (chives, etc). Another lady said NO NO, nothing, just salt and pepper.

And the neeps, turnips. Yellow, not white? Peel, boil and mash? Anything else go into them? Again, how many pounds?

This will just be a taste, as we are having a regular dinner too.

Advice, all ye Scottish chefs, please.

Thanks.

Susan
Slainte Mhath