If we tell you.....we must kill you. Every coach has a different theory. There isn't a true science and there isn't really a formulae per se.
Like Guido said before, there isn't really one formula that everyone goes with...
Over the years I've seen teams putting all 8 girls up front and then the 12 guys behind them with the biggest two doing Seat 6 duties... Also I've seen seating arrangements based on paddling experience with the rear few seats for newcomers. I've also seen teams that would ensure that the weight distribution was equal between the rights and lefts by way of asking for everyone's weights. As well they would pair up each seat with matching weights. For example if Seat 8 Left was 200lbs, they would find someone one the team that would be roughly 200lbs. Usually teams that use this method have ambi-paddlers.
As some pointers, it's probably best to get outside of your boat when it's on the water and see how it sits on the water. If it's bow heavy (front-heavy), then it's would probably be a good idea to move some weight to the back and ensuring that the left and right is balanced. As long as those terms are satisfied you should be ok.
