Around WSO there seems to be a general consensus for what is considered the “correct” abbreviations: K for Thousands. MM or M for Millions.
Once you have 10k followers, Instagram will make it easier for you to get people to your website via Stories with the swipe up to link feature. Swipe up is the only way to get a direct link from your Instagram to your other web properties. And, it’s available in STORIES, if you have 10k followers.