Sour cream plus extra seasoning yields that old-school deli flavor.
Convince yourself that adding this much extra sugar and salt to store-bought mayonnaise is not a misprint, then chop the dill and mix everything all together.
OK, let's talk - you can scale back on the sugar and salt if you just can't stand yourself otherwise, but give it a try this way. You can always add more mayo and sour cream.
In terms of the ingredients, I think homemade mayonnaise is a waste here. I use Hellman's/Best Foods. Their light version is pretty OK with me, even in this, but I highly recommend using full-fat sour cream. For vinegar, something not too flavored and not too dark is good - white wine vinegar (as pictured), cider, or just plain white. Dill is optional, fresh or dried - you can always add it to the salad itself.
This dressing will keep for at least a week or two. I do like to make it separate as I prefer the just-in-time, just-enough approach to making potato salad and cole slaw. But this is because I often add things like pumpkin seeds or currants that will swell up or get soggy after a long day's night in the fridge.
And finally - this much dressing can make anything from 1 1/2 to 2 pounds of cole slaw or potato salad, depending on how wet and rich you like such things.