You have posted very exhaustive requirements and a valid one.
I am wondering, does a UI/UX expert know this much about business to help you out? I think you need a product manager.
How I can help? I would put my self in end user shoes and navigate through your site to suggest the challenges and issues. Then suggest the relevant changes.
Coming to the other part of marketing strategy and customer engagement, I think that requires more study of your targeted customer base.
I don't have experience in this aspects as such, however, I have been product owner and to think the way customer think is my bread and butter. I think, would be in a position to help you out.
How you can manage the risk of working with me? First 5 hours of work comes with money back guarantee.
Seems interesting, then let's talk.
Many Thanks,
Shubham