I have an website that get news from RSS Feeds. I build every day 2-3k articles and now i have almost 160k links.
So, how often i should re-submit the xml sitemap; (currently i do this job every hour)
Depending on your server configuration you can setup your site to run cron more often.
You can also use Rules module, To write a rule for resubmitting site map which can be trigger after certain time or on new content published.
It is also important to mention that search engines takes time to index - no matter whether through external links, internal links or sitemaps.
So don't think submitting site map more often will help.