Dont read if you're looking for a service/someone to do everything for you
My friend sent me to a website that helps with marketing and consulting for Amazon. Im launching a clothing line on using Amazon and I already have a ton of pre-orders, but there consultations definitely made a difference, especially with the SEO and it was pretty cheap as they work with your budget because they're not in it for the money. Try them out and use my name as a reference to get a free consultation and possibly a great deal on their services.
This is their site Digitalassimilation.com
Best of luck