The method of feeding you use depends on what kind of eater you have. Free feeding only seems to work for dogs that only eat to live (I tried it with Roxy, but she ate it all at once). :P
If you like the idea of free feeding but would rather scheduled feeding, I would suggest small frequent feedings, like 4-6 times a day. However, I feed Roxy 3 times a day because she wouldn't be satisfied with such small feedings. To measure out how much food she gets each day, I start by measuring out according to the serving suggestion (give or take, again depending on dog) and then put it in a baggie.
And about what veggies you shouldn't feed, I think there is a pinned topic about what foods are poisonous for dogs. I feed Roxy carrots, green beans, and yogurt with her food on the weekends and just yogurt mixed in on the week days.
I guess I would only worry about hypoglycemia if she didn't eat, but for the first week I gave Roxy Nutrical before or after she ate (I forget). :P
Hope I helped!
I am definitely no expert.