I would have to agree with lauralee on this one. I would run the tank fallow(fishless) for at least a month. Heck, even some say that would be rushing it, and to be on the safe side, go fishless for at least 6 weeks to be sure that it goes through it's life-cycle and without a fish host to help it reproduce, it would die off. I wouldn't bother moving your plants at all, as ich can live for a brief period of time on wet surfaces you risk spreading the contamination to your other tanks that come in contact with even the slightest amount of water from the infected tank.
I would not place them in your tank with the ottos. Also I've never heard of getting rid of ich by going dark.