9 times Zazzle? I doubt that, though I've no idea what Zazzle pays. Amazon has info on what it pays on its site. Basically they take the first X$ then a % of all $ above that. It is up to you what price you set. The X$ varies depending on the type of garment you are using. Merch by Amazon is not a get rich quick scheme, despite all the YouTube videos (which are actually people making money from YouTube ad revenue, not MBA!). Amazon gets most of the money; they are also doing all of the work other than posting up the design.
You do not get a store on Amazon with MBA. Each design/shirt stands on its own. 99% of the point of being on Amazon is BEING ON AMAZON. Nothing you can afford to do on your own is going to be worthwhile compared to natural traffic and SEO on Amazon.
Carefully read the MBA policies. Your design cannot contain any IP that you do not have the rights to, nor can you mention any trademark or celebrity, dirty words, etc in your listing text. They have bots that check for this and automatically reject such listings. Also, finding some older design on MBA that got away with something proves nothing other than that they continuously improve their bots and you won't be able to get away with that today. They'll close your account if you persist in violating policy, so try hard to avoid doing so. 2 of my first 3 designs got rejected for policy violations, and I was NOT trying to get away with anything. I just wasn't paying close enough attention to what their policies really mean. Lots of people cry and whine about how MBA enforces this; too bad for them. It is MBA's rules, and MBA's game. Learn the rules.
Keywords are just the words in the listing Title and in the 2 bullet points you can add to the listing. Those lead to your listing when someone uses the same or similar keywords when searching with Google/Bing/etc or the Search tool on Amazon. FYI If you put up a design that in no way relates to anything that anyone is likely to search for, then it will NEVER be found. People can only find what they search for, and closely related things. Your depiction of your aunt Bee may be stunning and startling, but is unlikely to be a hot search item.
EDIT: It took me over a year to get accepted. They have since changed the application process to put more emphasis on people who have an existing line of designs that are already being sold somewhere. And the process seems to move more quickly now. Though that could all change tomorrow if they run short on capacity again (until the next upscaling, if there is one).