Sounds like you're off to a Great start!
RMB - Raw Meaty Bones
MM - Muscle Meat (includes heart)
OM - Organ meat (liver, kidneys...)
Bones, as I recall should make up about 10% of the diet...but that's tough to guess, isn't it. I think the formula Lauri puts on her website will get you there without you having to guess what might equal 10%: The Basics
As I understand it, if you're feeding PMR (prey model raw) you want to approximate the proportions that would replicate feeding a whole prey animal (hence the ~10% bone). Doesn't need to be done every day, you can make up the prey animals by combining separate parts over a week or so.
My rule of thumb is that if my dogs' stools are too firm, I'm feeding too much bone...Too loose, too much rich organ meat. You'll find yourself inspecting stools and being proud of yourself when they are Just right
The goal is stools that are firm and compact, but not difficult for the dog to pass. They should turn white after a couple of days and start to crumble (if you have enough property where you don't feel the need to scoop up every poop right away you'll see this happening).
But, you might be working more on the B.A.R.F. model, since you're feeding veggies, in which case my response might not be too helpful.
As far as gulping goes, try freezing the chicken parts first. It forces them to chew thorugh the meat and bone at the same time and helps lessen the chance of them gulping a bone. Also, larger parts make them work to tear the meat off the bone and can lessen the chance of them gulping bone, at least until they work it down to gulping size (which you can monitor for).
What to completely avoid: Dense weight bearing bones from large animals such as cow femurs. These are known as "wreck bones" (many people give them a rec/recreational bones...these are the things you see in the pet stores and feed stores. I quit giving those a while back. The reason is that they can be tooth-breakers. If you want to feed a large animal part like this, just let them eat off the meat and take the bone back and dispose of it. And I think twice about cut bones, like found in a t-bone steak. I try to stick with natural animal parts, like they would encounter naturally when eating prey animals.