Well your goal should be to unlock them all. Not to use them but to level them with potions. Thats the best way to gain power.

When you get a new card dont waste cultivation pills unless you are planning to use it. Some cards are really good for specific teams. Like for kakuzu you should use Onoki card. Or for Kushina or Naruto 6p you should be using Gaara card. Cards like that should be maxed with the pills.

If you change teams a lot but you dont have cultivation pills to level all cards then Tenten is a good choice. Critical is a good offensive and defensive stat.

But as i said you should try to get them all. And your power will increase fast

Well in my opinion Gaara is a lot better then Temari for Kushina team. But if you dont have pills it really doesnt matter what card you get next.

It seems you are F2P so try to unlock all cards as fast as you can. Every week you can get few command flag frags for free so always go for them instead of ninja frags. And then try to level them to lvl 3-5 with potions.