Its a good idea for sure, however you have quite alot of things that need to be fixed as it is incorrect. For example magatamas have nothing to do with combo or as you call it "combostreak". They affect base stats only.

As for spending coupons, the most efficent way is always low cost high return events like for example lucky board. Now as a general rule of thumb i like saying you should always spend for what you personally want. It could be ninjas or anything regarding power. But you should never let someone else tell you what to spend for as only you can know how you want to play and what you want.

As for group skills upgrading them all equally is a great idea for sure! However you should try focusing on getting them up to the max of your group one by one before just distributing across the board equally.

As for mood its usually dependant on the growth values what gives you the highest return. This can be easily checked by having them in your team and clicking details under character.

Keeping everything equally upgraded is a good way for sure, however keeping mood's etc maxed on every ninja is very costly especially considering you will probably switch out ninjas frequently when you want to use new teams or get a new ninja you like. My personal recommendation is maxing the mood on main first and foremost and not going above 25% on any ninja you are not planning on using for a while.

As for summons you imbed the runes into the actual slots not the summons, as you can switch out the summons and the runes are still there increasing power. (all 3 of the summon slots can have runes in them and they will all increase power).

Well done nonetheless and i hope to see you update this /Achroma