Personally I have avoided the amazon affiliate program. To me it only makes sense to use amazon if there is no other affiliate program option for that niche. The 24 hour cookie time is brutal since others do 30-90 days. I would think for decor people need way more time than 1 day. There is almost always an affiliate program offering higher commission with better terms in any niche. It’s just a matter of finding the best ones to promote.
Yes is the short answer. Any time you are planing on generating money, you should have a plan. No plan means no real focus. There may be some 1/1000 percent of a chance you will succeed, but I haven't met them yet. If you have already started and have generated an income, record how. Doing so will give you material for use in expanding your business faster.
In that online affiliate marketing course, they will teach you everything you need to know to run a business online everything you need, even you'll learn how to create affiliate campaigns from scratch even if you currently don't have an audience or a list and the best part is you don't even need your own products to make money with affiliate marketing.
The amount of money you can make can depend greatly of you budget. If you have a small budget and you don´t have a lot of money, then you have to start with free marketing methods like article writing, blogging, forum marketing and such. It takes a lot more effort ant time to have success with these methods. But they are very effective if you keep writing articles and participate in forums. You can make $100 a day within just a few months just with article marketing.