If you are using 2 PSU's then you will need that multi-PSU Adaptor.  What it does is detect when the first one is turned on and then it switches on the second power supply.  Without it, the second power supply will not turn on when you turn on your computer.

Forget about the PCI slot, and use one of the SIX video cards for the monitor.  (It won't affect your mining)

and yes, you'll need PCI riser cables, try and get powered ones if you can, as video cards still draw some power from the PCI-E slot even though they have additional power connections.  With out it, operation can be unpredictable.

Everything else you are wondering is covered here:

http://www.cryptobadger.com/2013/04/build-a-litecoin-mining-rig-hardware