I need a Sitemap.xml expert

I am looking for someone with experience on sitemaps for large websites. I have a website with more than 100,000 pages and I need them to be indexed in the sitemap. Please tell me why you are qualified for this job.

I have attached my latest sitemap but it's only crawling 999 pages. I need to crawl all pages. This means that the sitemap will exceed 50MB and I need someone experienced to deal with that.

Please provide examples of previous work and demonstrate your understanding of sitemap.xml best practices.