Many affiliates test 20 campaigns before finally finding one that actually makes money. You can drastically increase your chances of success by taking your time and doing things right. I don't recommend you go out and build out 20 or 30 niche sites to test campaigns!
Once we get into the paid traffic stuff you can test multiple different niches and offers without having to build your authority site first. Once you find an offer converting extremely well then you can consider building another authority site or just ramping up the paid campaign.