Ok so i think i bit off more than i can chew. I was kinda hoping she would back out but she just paid me to do it. OMG I hope i don't mess this one up.

I just got the pans the sizes are 6x6x3, 10x10x3, 12x12x3 How much box cake mix do i need for these? and how long to cook them at and what temp?

Also any other tips you can give me will be SUPER help

The cakes are square i have never in my life put fondant on sqaure cakes. I heard on this post that they used vinyl to roll the fondant on and it didn't stick at all. Dose it really work. I see on Cake boss they have a gray mat that they just roll the fondant on and flip it on the cake with out any sticking it that basicly what it is??

Thank you SO much for all the help. I was trying to send picture but it will not let me for some reason.

Oh by the way I am also doing a grooms cake in the shape of a baseball hat. Any tips on how to do the bill of the hat?? i dont have any picture of that

I don't do box cakes but the way I would do it is count the servings in each box and then count how many servings your pan will yield. Divide the box servings by the pan servings and you will have it. I would do a couple extra just to be safe. They only cost 2 bucks anyway.
I think with the temp you should go with 325 and as for time..... just watch it like a hawk. That's what I do no matter what I am baking.
This cake doesn't look like fondant. It also has a ton of non-edible decorations on it. Shouldn't be that hard. Once you get the cake squared away and stacked you are golden. Have fun.

Everything you need to know to make, decorate and assemble tiered/stacked/layer cakes:

http://www.cakecentral.com/cake-decorating-ftopict-605188-.html

Above superthread has popular CC recipes for crusting American buttercreams, several types of fondant and doctored cake mix (WASC and other flavor variations) - and so much more!

One of the links will take you to Wilton's cake making help. Charts give batter requirements by pan sizes as well as recommended baking times and temps. and serving yields by pan size.

FYI, I find it easier and faster to bake two 2" layers than one 3" layer.

HTH