OK, to break it down for you.
Lights
MH is for veg. HPS is much better for flower but MH will work.
Your 600W MH light would your plants MUCH more light so you should be using that after about a week or from seedlings if you can keep it a goodly distance away.
Normally I would say get an HPS conversion bulb but that's $100 so I would spend a little more and just get a whole new setup. And in the future don't buy MH ballasts, buy HPS ballasts because MH conversion bulbs are MUCH cheaper than HPS conversion bulbs.
Also if you get a digital ballast make sure it works with both kinds of bulbs via an MH conversion bulb.
Cloning
You can move the mother plant back and forth between the different lights without any problems. Just make sure you aren't changing the light cycle, that's what can mess her up. You don't want to have a plant go into flower then take it out of flower. It's do able but not advisable to do so because you might hermie the plant.
A mother plant will be fine under floros. In fact that's a great place for her because you don't need her to grow that much, just enough to give you plenty of new growth shoots to clone from.
