You do understand, you just are not positive you understand. Pretty normal situation around here.
Yes, using CBR for a short video at 8Mbps using the highest quality is fine for what you want to do. There is no need for a second pass to optimize the quality if it is using the maximum rate.
Don’t be tempted to use a higher bitrate since there could be players that have trouble with anything too high.
Steven
https://www.stevengotz.com