1. Yes, you can counter it. Use regular negation for it or 'loop' a negation.
2. Hmm... there is no traditional way of dealing with them, but this is how I do it. I decrease my own power or increase opponent's power until their power is higher than mine- then I use my advantage. As long as your power is lower with advantage you are good.
Other way would be use 'copy' or 'reuse' effect to get something from the field that would be useful against advantage. Or use 'loop' to indirectly negate advantage. 'Loop' is basically selecting an effect that exists in your Bakupack and using it without applying its cost to your limit counts.
Idk... that's my experience. Advantage has never bothered me much. When people overuse it you eventually know they're gonna use it again so you're ready.