A tablespoon or something does the trick.
I made Barf-patties that I feed almost every day. They have all the supplements (including yogurt).
As for veggies, celery is pointless IMO. I wouldnt feed it. Go easy with the carrots because they have alot of sugar. Squash is good. Greens are good.
I buy a Oma's Pride 5-way veggie mix. I forget what the veggies are. Squash, kale, broccoli.... I forget. I'll let you know when I buy it again.