craftgrrl | Food Craft and Question

Link to the Pictures
I'll be making these little meringue porings (a monster from a game called Ragnarok Online - if you google image the word poring, you'll come across lots of original pictures from the game and such to compare my creation to) for an up and coming anime convention.

So I present to you my little poring army. =3 I'm quite proud of them. Especially the little girl one hidden amongst the men there.

However I do have a few questions related to meringues if anybody has ever dealt with them before.

My meringues cracked in the oven. Now I've heard that opening the oven door even a crack will cause this however the second batch I made I didn't go near the oven and they still cracked. I heard that cream of tartar improves meringue quality but after adding it the cracks appeared. In the first ever batch of meringues I made, there were no cracks so my question is what does the cream of tartar do exactly? I don't think I'll be using it in future batches though.

And I can't get my porings to cook all the way through. There is a little squishy part on the inside that just doesn't bake through and the innard breaks away from the hardened outer shell. I've been told by a few people that this doesn't matter and meringues are good that way anyway (seeing as how they are actually cooked all the way through) I just wonder if maybe there's something I could do to get them more professional like on the inside as well as outside.

Thanks =3

Oh and if anybody is wondering, the recipe that I used:
4 egg whites
1 cup of castor sugar
pinch of cream of tartar
vanilla essence
food colouring
I used basically the same meringue method that's found on a lot of websites and baked it in the oven at 120degreesC for about just a little over an hour.

I hate my oven..the bottom shelf, back few rows always get burnt bottoms. But I'm too afraid to get into the oven and turn the porings around in case something weird happens to the meringues.