I don't like the 'you can't switch twice in a row' thing. Most probably, everyone would end up attacking, then switching, then attacking, then switching, etc. Plus, as you have already noted, Focus Punch will be broken (although this can be solved by not putting Focus Punch in any of the movesets).
I propose a limit on the amount of switches. For example, no more than 10 switches is allowed per game per player. Or change that number to whatever is deemed fine.