I have a content site and I want to launch a department store, but I have over 5000 products.
I want to launch a department store with Craft CMS; of course, my blog's section is WordPress.
Is this possible?
Yes it's possible.
You're kind of making more work for yourself by keeping the blog on one platform and the store on another but there is no reason you can't do it that way.
You will need to run the blog and the store on separate domains i.e.
shop.yoursite.com or else move the blog over to Craft (or run your store on Wordpress).
There will be extra challenges involved if you want to share data between the 2 sites - because they will effectively be 2 separate websites. But again, totally possible with the right planning.
Commerce will cope fine with 5000 products.