1. Wait and save. Coupons don't lose their value over time. Ninjas will come back eventually

2. In every single case go for permament seal rebate. 66 scrolls for 300 VS 40(44?)+2hashi frags for 500. You will get those 2 frags from bonus seals you get from permement one anyway, but you also gain more seals overall, more frags and stuff.

3. If your group has both really good atmosphere and you arent super competitive, just stay as your own group. As long as previous criteria are met, you feel fine playing as it is and you actually can find teams and do all activities- merging for the sake of merging makes no sense. Ask your group for opinion first and foremost. As you said, merge also reduces seal income by a lot.