The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.
Paid ads should be your last step in marketing your range of affiliate products. You want to make sure you’re in a money-making niche and have a roster of products proven to sell, as well as proven sales funnel that compels your prospects to buy. That way when you invest the money in a paid ad, which can cost hundreds and thousands of dollars, you’ll see a decent return on investment.
Thanks Nathalie! And glad to see you came over from AONC 🙂 When done the right way I think affiliate links in context are much less intrusive and offensive than having ads on your sidebar. The average non-tech reader probably wont even know its an affiliate link anyway. So just by doing everything you’ve already been doing, you can switch out links, and probably make a nice side income!