just to pick up on Ashley's point, I have had GD of 106 and 94, at lvls 62 & 64 (if memory serves). It can be done as some leagues are weak at those levels. If a team had that kind of GD after lvl 70, that would be suspicious.
Brotherhood: I think some of your points you have made are correct. It seems at the start of a new season, if you've had a 2 lvl promotion, you have to adjust. Which isn't logical. I would presume most have the full 'kit' at the end of the previous season (giving, supposedly, a 3 level boost), so adapting should not be a concern, but it is! I think the 'sports kit' doesn't have the desired effect, but I can't take the risk of not having it.
Your point about kicking the ball into your own net. Did you have players stationed on the line? What can happen is they can pick up the ball in the six yard box and then travel back to their 'starting' position and score an own goal that way. I discovered this accidently by playing a team in a friendly, before a cup game. So, I adapted my tactic to cross the ball into the box, with no forwards to receive, the oppo scored 3 own goals! This was last season, it's a shame I couldn't 'keep' the match.