Well, im planning on building an acrylic case
and here are some diagrams

I say go for it ! I would use a 120 in the front instead of 2 80's though.

well....the 2x80 pushes more air and is louder (on average) but the 120mm is quieter

you could do 2 120's stacked on top of each other. Also, try putting the side intake fan over the cpu hsf so that cool air goes directly to it

i was thinking about putting 2... one that has a tube that takes directly to the cpu
and another one... just to intake

I can see from the rear view this is going to be a full tower, 3-80mm fans will take a lot of space.

here's a little apetizer for your project

http://forums.bit-tech.net/showthread.php?t=46844

HELLLA LOUD!!!!, i say you should get a fan controller with it get 2 120mmm then 3 of the loud 80mm plus 120 moves much more thant he small 80mm.