1. No real Gacha, you need crystals and shards to roll for units;
1A. Crystals you get from finishing the daily quests(Didn't really pay attention, but you get at least 1 each day) and some dungeons;
1B. Shards are mainly obtained by having friends (Gives 10 instead of 5), though there is a level that gives it.
2. The current 2 events are easy, you can finish them nearly right after unlocking it (Get to 1-7-2); it's also pretty useful for grinding.
3. If you roll the 10x Gacha, you'll get an extra guaranteed SSR; I also heard that once you max out a character's class, they are taken out of the pool, so that'll increase your chances. Edit: You are refunded their cost.
4. Dupes in this game are used to increase the level limit; though the equips are annoying to max; though the weapons are annoying to max.