Some suggestions.

1.Level 2s are just there for the FG for max affection and to round out your group until you have 3+ rankers in there. I say level them using basic manyuus until say 20 or so and then just keep them for the World Map challenges

2.3 Rankers will be your backbone until you get a good stable or 4-5s, max leveling them isn't that bad an idea

3.Special events? These do require a good team to take on the ultimate ranks, thankfully you can hold off now that they are reprints

4.Don't use FGs to restore stamina or raid points, practice being patient

5. Concentrate! Spreading out the rewards just slows things down. Toss the power ups into one until they are maxed out. Plus getting a full team of the required FGs to exploit weaknesses is unlikely.

6.Later on, it starts boiling down to what FGs you really like. Design, attack animations for instance,. I like the rocket hammer Sakura and Electric Chainsaw Wax vine