Okay I can give mine now, I think season 2 should not go down the SV route simply because 22 characters is too much and none would get developed enough and as I said before you could not have Rin against Homura as she was on their side this time.
One main thing is they should have done more episodes this would of allowed events to be more natural and not so rushed, plus it would have allowed the characters to be better developed. With more episodes it would have allowed fights to be given justice rather than talk do nippo talk other does nippo, distraction, fight ends, another budget would have been an issue but fights like dragon ball which went over more than 1 episode would have worked well.
They should have more interacting between characters from the different schools to see how they would relate and would reveal more about the character, going off this Katsu-nee shouldn't be so constant on Asuka in the manga she goes for anyone.
I mean wouldn't seeing that scene and this scene both be funny and insightful on how the hebi girls would react especially Homura as I would of thought she would of sent katsu-nee flying but apparently not meaning you might get to see Homuras sensitive side. If not then I guess I just like Katsu-nees antics.
As for approach I’m not sure about this one but for the first they should have started at Spark and had that last 3/4 episodes then work their way to main story it would made the story have a lot more development, plus if I knew nothing about the series I would of wanted to keep watching to see who are those characters they keep showing in the intro especially Asuka as she is the main but wouldn't appear till ep3.
Lastly as much as I love the Hanzou girls the story have been a bit more even between the 2 schools so the hebi girls didn't seem so 1 dimensional and showed them fully e.g how sweet Yomi is and that she can just lose it.
My original idea for the next story and could be for the anime is to have the girls all join Hanzo school. This would lead to more interaction and better fan service. The other group they are after should remain a secret until the end when you find out its the other school form SV there by setting up the thrid season. Throw in some newwave girls as backround characters or cameos and we are good to go.
I would remove characters at that point. Don't need to tell all those stories now just tell the one side then tell the other if there is another season. Problem with all of this planning is you can never tell if your show will get another season to finish everything off.