By spending as much money as you can like everyone else in this game does..

^ same, i have most equips (not tier 4) but still.. i totally regret not waiting for father and son skin

Nvm, i got it fml... but now it says card not fully owned when I uprgade it.

Will the F&S skin improve my sage naruto much or should I spend the 15k gold on something else?

If I only have sage naruto but have 15000 gold can I get strongest f&s or do I need kurama naruto?