Well as far I know to get Gaara u need curent ingame cash recharge event, so he will be 4 star.But its only 2 day left and if u didnt get reachards and its rewards since start You cant get Gaara.Dont know if its the only way, but some mod said some of characters are event only.

I already got Gaara just need to know what the order of attack is for best combos. Say like Gaara first then Kank-main-tem etc?

Well it all depends on opponent and what you need at the moment. Usually i would go with kankuro puppet firs as it guard quite well and do much more dmg than kankuro alone

Go with Gaara 3 star or 4 / Kankuro and Temari. Every Character you can get in a event only will be added later after 1-3 month into the game availible for all. It will be in a treasure too draw or at a redemption shop for coins. So not only casher can get a specific character its just they get them i little bit early cause they pay.