You can do all of that.
Using -d # (devices) with most miners to set which cards to use (eg. -d 0,1 will use both cards to mine).
But I think you need to turn SLI off in the nvidia driver for mining.
I'm a bit illiterate with the .bat files. So using "-d 0" should work only the first GPU, and using "-d 1" should work only the second, and I am guessing that with "-d 0,1" the miner won't know to run both or all cards by default?
Just checking if lets say I had my current 1070 mining ZEC with one miner and an RX card mining ETH or XMR?
I can do without SLI. I don't need any more power for personal use beyond what my single 1070 performs. It's phenomenal on a 1080p 60hz monitor