xD yeah, wifi is weird like that. But I guess it makes sense that they let you pick however many you want, not like - force you either way. But yes; normal rules dictates 1-6 for Singles, 2-6 for doubles. And it sets them all to level 50 ^^
If you wanna good practice round, 6 v 6 would work best since it's what everyone else in that league is gonna be playing. I'll let you know my team beforehand too for fairness sake.