I don't have all the answers but I believe I have a few for you -
I don't know of any software for measuring energy usage, but you can get a meter that will measure it at the wall for just a few dollars. I personally purchased this:
http://www.amazon.com/gp/product/B007KX2YXQ/ref=oh_details_o03_s00_i00?ie=UTF8&psc=1The only platform I've discovered so far for litecoins is btc-e:
https://btc-e.com/I cannot speak to their reputation personally as I've never used them, but they do have a large thread here with lots of comments if you want to do some research:
https://bitcointalk.org/index.php?topic=40889.0I have not had any problems splitting up video cards as you suggested (disabled Xfire in my base with 7970s) and mining from the GPUs that weren't connected to my monitor while using the remaining GPU to do whatever (I don't game on it, but I do watch movies and such). I personally use 50btc:
https://50btc.combecause it's ridiculously easy to get started with their GUI miner, and it has a throttle so you can use all of your GPUs and just throttle it down so your computer isn't crashing when you watch a video or do anything else, plus the pool fee's seem reasonable to me. You can instantly withdraw your BTC anytime you choose to as long as you've accumulated at least .01.
I've never mined any litecoins so I can't really help you out there either.
I have measured my 7970 x2 setup pulling ~660w at the wall with a 1050mhz overclock on each card (setup with i5 ivybridge + watercooling loop that I'm sure takes lots of extra watts). Most suggest to keep a PSU at about 20% below it's max for power efficiency and longevity, but it totally depends on the quality of your PSU.
Hope that helped.