Adding any emoji as a reaction remains under review.
I am marking this as partially done to let you know a new reactions bar with Like, Heart, Laugh, Surprised, Sad, and Angry has begun rolling out to all users.
This item is still under consideration by the feature team.
The team has updated the default sound for Teams notifications so it is more noticeable. We are in final testing, with a goal to release the new sound by the end of this quarter.
Once support for Windows 10 native notifications is released, users who choose to use Windows notifications will be able to utilize Windows OS specific settings for the length of time to display notifications. Mac does not have an OS specific setting, so will not have the support.