My cats both nibble grass and one likes to eat some catnip from time to time. I can always tell when they've eaten any grass however, because it comes out of them looking pretty much exactly the same as how it went in. My one cat swallows it whole and sometimes has trouble passing it, so I try to limit how much she gets. I'm not sure what either of them actually get out of eating grass because they definitely don't digest it. But they seem to like it so I figure it's probably fine as long as they don't eat too much.
Anyway, in my opinion your recipe is not balanced. It's a good start, but you should be aware that heart is high in sodium as well as taurine. My cats get heart a couple times a week, but they also get other kinds of meat. I think using heart as the main muscle meat in this recipe (if you intend to feed them this as a main food every day) would give your cats far too much sodium per day. For more information you should read this article: Answers: How Much Heart is Too Much?
Just so you know the harder a muscle works the more taurine is found in that cut of meat. Chicken thighs have more taurine than chicken breast, and I've seen chicken thighs recommended for a lot of ground raw food recipes. It can be good to start your cats off on one kind of meat, like chicken.
You must have a pretty heavy duty meat grinder if you're planning to grind turkey necks! Those things are huge. You would need to grind it well, because I don't think there are many cats out there that could tackle a turkey neck whole. If you can grind turkey necks you should also be able to grind the bones in chicken thighs much easier. The ground raw food recipe at catinfo.org calls for chicken thigh bones. If your plan is to grind their food you should check out the info on that site.
If I was going to make a ground raw diet for my cats I think I would stick pretty closely to 80% muscle meat, 10% bone, 5% liver, 5% other organ (I usually use kidney or spleen). Raw feeders recommend that ratio because it's about the ratio of meat to bone to organ found in small prey animals like mice. I feed franken prey and do not use any supplements (my cats do get the occasional egg yolk or canned sardines for omega 3s) and they're doing great! Unless you want to add some taurine there really is no need to make it more complicated than that.
Anyway do make sure not to use too much liver, as liver is rich in vitamin a. Too much vitamin a can cause a condition known as vitamin a toxicity or hypervitaminosis a. Just 5% of your cat's diet should be make up of liver. For instance my older cat eats 21 ounces of food per week - and each week she gets about 1 ounce of liver.
You also shouldn't use whole eggs. Raw egg yolks are great to feed occasionally and I've seen them used in ground raw food recipes, but raw egg whites should be limited because they are high in avidin. Avidin binds to and blocks the absorption of biotin (one of the B vitamins), which can lead to biotin deficiency. I doubt that the occasional egg white would cause this but I wouldn't advise feeding raw eggs whites to your cats every day.
As for the pumpkin seeds? I honestly don't see the point in adding them. I guess you can if you want to, but think about how small a mouse or bird's stomach is. That and maybe a few blades of grass is all the plant matter a cat would eat in a day. Plus whatever is in a mouse's stomach would be at least partially digested before a cat would ever eat it. Raw pumpkin seeds in that quantity really don't resemble what a cat would eat naturally. I'd really suggest ditching them from the recipe all together.
People usually recommend adding Salmon oil to raw food (for the omega 3s), but I really don't think any kind of plant oil is going to have the same effect as animal oil to an obligate carnivore. As for fibre, I believe the raw food recipe at catinfo.org does call for psyllium (the stuff metamucil is made of). I don't feed my cats any plant fibre and my cats have never needed any. When I first switched them to raw they had problems with constipation, so I started giving them a little less bone and the problem was solved. That's not to say no cat ever needs fibre or even that you shouldn't use it if you want to, I can only tell you my experience. I'm also wary of using metamucil every day unless a cat really needs it, because right on the bottle it does warn not to over use it. Your body can become dependent on it, so I would think a cat's body could also become dependent on it. Just my two cents.
It's a great sign that your cats are willing to eat little tidbits of raw! They should take to it right away when you make the switch. Right now you can give them chunks of any kind of raw meat you want, as long as plain raw meat doesn't make up more than 15% of their overall diet. My understanding is if they're eating more than 15% raw you should start trying to balance it with bone and organ. Just like too much bone can cause constipation, too little can cause loose stool. Nobody wants that!