I'm not sure if this is a very extended comment or an actual answer, but here goes...
Your planet, as you describe it, cannot possibly support life. Of any kind.
Ultimately, a planet that supports life needs two things; a plentiful element of high valency, and an oxidising element. Let's deal with this latter one first.
As the term suggests, the most common oxidiser out there (by far) is oxygen. This is an element that reacts with other elements to release energy out of chemical bonds. In respiration, earth based animals breathe in oxygen, mix it with carbohydrates to produce both water and CO2. These compounds are in a lower energy state, meaning that the conversion from sugars and molecular oxygen to water and carbon-dioxide has released energy, which the animal uses to live. You can also use other elements, like flourine, but in the vast majority of instances oxygen is going to be the element you use because generally speaking (not a hard and fast rule) the lower the atomic number of your element, the more prevalent it is in the universe.
Either way; without some form of oxidising element, you can't have life.
Now let's deal with valency. We're called carbon based life forms because carbon as an element has a valency of 4. I won't spell out the details of this other than to say that this is a fancy way of saying that you can connect more atoms together with carbon than you need carbon atoms, which in turn means that those hideously complicated organic compounds are now possible. Elements with a valency of 2 (for example) can't support life because there's a limit to the molecular complexity that they can support.
Now, Silicon and (in certain situations) Chromium are also high valency elements, but again carbon is the most prevalent in the universe, and your planet with a high amount of diamond means a high amount of carbon. But, it's locked up in a crystalline form and you really need carbon to be freer in your environment to support life.
So; your planet has to have oxygen and carbon in large amounts to support life. There also has to be other elements, but those are the ones that really count unless you're getting really exotic and creating silicon based flourine breathing life, which might actually work on your planet (but I digress).
Ultimately, there are limits to your planetary design, and I've already written a primer in xenobiology for another question, which might also be useful for you in designing your planet. The important point though is that if you have a carbon based life, you still need oxygen, and the carbon can't be locked up in crystalline lattices that don't wear down releasing freer carbon forms into the environment.