It's simple luck, I've seen people get those 80 frag ninjas in this wheel for a mere amount of 200 coupons, and I've seen people not get them for 40000 ingots

No one can determine how much you will need

Wheel event are generally the most random, really depends since some basically end up giving one in total while others give it out dozens of times to even low spins. Just luck and resources is the only way right now.