In response to Hentai:

Keep in mind that you actually do not need anything above 3* to beat the game (though this was before 14-x was released, so who knows). A couple of 4* and 5*s, then the rest below that are all you need. Needless to say, everyone must be 100% affection, evolved and with mid grade equipments (though all of this are mid-late game things, so everything at it's appropriate time) Anything else is a privilege/luck. Event girls are the exception. As long as you are persistent enough, you'll get them as well.

If it's not too late for you, it's recommended that you get Lavender. Shes an A-B class 5* (B for the low speed). Maybe a bit too late since the event is going to end soon, but we won't know till we try, that's for sure. If not, then get Mirabilis.

Also, if you try Idol Wars and do the Dream Fest thing (this is only for the ongoing crossover, no more after it ends), you can get up to 2 5* tickets. So there's that as well.

As for the Flower Gems here's the deal: Logins, Events, Campaign, Special Missions, achieving 100% affection with any girl, and gathers (very rare, but possible). Flower Gems are premium ingame currency, so unless you're willing to pull out the credit card, that's all you'll get.

Always farm beginner stages when it comes to events. Even high level players do them occasionally when they're done farming ampys and/or crystals.