Here's my suggestion. We need a total of eight people for a PO/PS-based war team, as the simulators are both easily operable.
5 War Team Members
3 Subs
We obviously need another seven or eight people for a Wi-Fi based war team. If we encounter another clan that heavily prefers wifi over PO, it will give us an edge in knowing instantly who to send and what they've got.
3-5 War Team Members
2 or 3 Subs
A Captain should be appointed for each war team, with a Manager deciding who leads what team, based on their management capabilities AND their battling skills.
Obviously the selection requirements will be different. A PO/PS War Captain will accept candidates based on skill in both battling and team-building.
A Wi-Fi Captain will have to be pickier, as Wi-Fi battles demand that all applicants have their own competant team that has already been assembled, trained, and tutored. The candidate in question will also be required to have a very thorough knowledge of what their Pokemon can do, along with being able to put together an effective blueprint of their team before they actually build it. In addition, they will also be needed to be highly flexible with their team, and able to make adjustments to fit the current standard of play (which shouldn't be a problem, as the Wi-Fi metagame doesn't change as easily as the PO/PS metagames do).
It'll also be interesting if we're able to gather participants that are effective battlers in other tiers than OU. That would make for pretty entertaining wars.
