we have a lot of pages that we want to create crawlable paths to. How many links are able to be crawled on 1 page for sitemap.html

Hey everyone, I have another question regarding duplicate content. We are planning on launching a new sector in our industry to satisfy a niche. Our main site works as a directory with listings with NAP. The new sector that we are launching will be taking all of the content on the main site and duplicating it on a subdomain for the new sector. We still want the subdomain to rank organically, but I'm having struggles between putting a rel=canonical back to main site, or doing a self-referencing canonical, but now I have duplicates. The other idea is to rewrite the content on each listing so that the menu items are still the same, but the listing description is different. Do you think this would be enough differentiating content that it won't be seen as a duplicate? Obviously make this to be part of the main site is the best option, but we can't do that unfortunately. Last question, what are the advantages or disadvantages of doing a subdomain?