Its fantastic that you are thinking about this, I also do it myself rather than pre-made.
Well veggies are not necessary, by necessary I mean that the only things they actually need are raw meaty bones, muscle meat and organ meat.
First of all I am going to mention that from the meats you are choosing to use, for the raw meaty bones go for rabbit ones as bones from both of the other animals (venision and buffalo) will be too dense for them to consume. Stick to one meat at first (for example the rabbit) and once you are sure they are ok (firm stools etc) with that you can introduce the other meats.
Other things are optional, although I do give raw eggs and live yogurt. I very rarely give fruit or veg but if I do have some that needs eating then I will puree it raw and mix it with meat. Ocasionally I give a little bit of chopped up fruit as a treat. Obviously no grapes, raisins or onions. A good thing to remember is that veggies grown below ground are stool firming and those grown above ground are stool loosening. So if you are pureeing a few then its good to have a mix of some from both group.
As long as you give them a variety of different protein sources you don't need to supplement. I do give salmon oil and vitamin e but thats not really dietary, it just seems to give their coats that extra something.
You can't really free feed raw no, because you would not know what different quantities of different foods each of your dogs had eaten. They should be fine being fed on a schedule and you can feed more than twice a day if you like.
Good luck, feel free to ask lots of questions
