You have to reach Founder Rank to be anywhere near this amount of credits earned. It's very doable without going for gold in everything though. There are 450 credits to be earned on each challenge. Making it a total of 5,400 credits. Each Gold in the challenge and mini challenges will earn you 90 credits (90x5=450) Silver will net you 45 credits and Bronze will be a mere 15 credits. The mini challenges will be the easiest way to earn the full 90 credits per challenge but if you are going for all gold anyway you will get this no problem.