After generating the site map, do you need to go back to global settings to hit the "update" or "built site map" button when new pages are added?
 
Can you edit the sitemap1.xml to add new links and change last mod dates manually?
 
Is "sitemap1.xml" the file to submit to Google Site Map?
 
Thanks!

"After generating the site map, do you need to go back to global settings to hit the "update" or "built site map" button when new pages are added?"
 
My site map automatically updates with new products or removed products.
 
I don't know about your other questions

On second thoughts, I'm not sure.
To find out, add some products and see if your site map automatically updates. That'll give you your answer.

I don't understand why viart coders do not use for example sitemap.php file for sitemap generation.