I'm a f2p also, I did 100-120 probably without using Tobi once. I was lucky to get Ningendo as a first rare from Tendo treasure. He is probably the most used ninja that i did use for the exams. Also gnw Kankuro was one of the most used aswell.

You don't really need to do exam exactly how the guide says. Just follow the base and try to get the best out of your ninjas. For example, Shikamaru can be a replacement for Ningendo. I used Ino in a lot of exams aswell, her chaos is gold.