I've decided that I really want a January 1st go live with the product data. Even though we are no-where near ready for checkouts, getting those product pages up and getting google indexing it is essential for long-term SEO.
I started by preparing lambda routines that would nightly prepare sitemaps for all the product data. Putting all the products into one sitemap would be too huge. It's also too much to process at once. So I organized the sitemaps by product category. Each category is processed one at a time, in-sequence for their products. A sitemap index identifies each.