1) Will my MOBO handle 6 GPUS? Anyone has this particular board? or at least something close to it? Would you recommend it?
Mobo will handle 6 GPUs, but you will need 3 x16 to x16 risers, and 3 x1 to x16 *powered* risers to handle all of the 6 cards.
2) Do i really need CPU for LTC mining? will this celeron work?
Almost any CPU will work for LTC mining, this one will be slower than the core iX series processors, but it will handle everything else fine.
3) 4GB ram per rig should be plenty?
4GB of RAM will require a 64 bit OS, and if you go the 4 GB per rig route, I recommend using two sticks of 2GB, as it will allow the rig to function a lot faster. Two smaller cards are always faster than one RAM card. Make sure the two cards are in slots 1 and 3.
4) I would use 2 PSU's per rig - will that work?, UNLESS YOU KNOW A BETTER(CHEAPER) ALTERNATIVE?
2 PSUs would be a lot safer and reach the power requirements of the 6 cards easily. That is the best way to go but please note, you still will need the x1 to x16 powered risers.
4.1) Do I need ADD2PSU to connect those two PSU's? http://www.add2psu.com/store/
That would work very nicely, but (Not sure, check me on this one) the only purpose to using two power supplies is to use the extra pcie connectors to power the cards. That ADD2PSU thing is mainly used in server motherboards.
5) will 3 powered extenders per board is  enough?
3 powered *x1 to x16* powered risers for the x1 slots is required. powered x16 to x16 risers aren't required, but will ensure that those cards reach their theoretical maximum hashpower. I don't believe the cards will have issues getting to max without them though so you won't need them.
5.1) Should i get powered 1x extenders or 16x(powered)?
Powered x1 to x16 risers are a requirement. You can't get around it.