Apache Busy worker thread increased to MaxRequestWorkers setting and getting error AH00286: server reached MaxRequestWorkers setting

Question

In our production Apache servers i am observing error AH00286: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting

My Environment:

I am using Apache Server version: Apache/2.4.18 (Ubuntu). MPM worker config as bellow.

<IfModule mpm_worker_module>
  ServerLimit         25
  StartServers        2
  ThreadLimit         64
  MaxClients          150
  MinSpareThreads     25
  MaxSpareThreads     75
  ThreadsPerChild     25
  MaxRequestsPerChild 0
  ListenBacklog       511
</IfModule>

During this time there are concurrent request observed to the server however the HTTP response code for all requests are 200 for almost all request excluding very few 302.

I am running Bitbucket server behind reverse proxy.

Question1) how to find my ListenBacklog that is 511 is getting filled OR how to identify its not enough?

Question2) How do i reproduce this error ( i have used AB tool in the past but seeking advice to on this)

Question3) When i get this error, will new user requests & existing user request which are in the queue will be rejected?

Question4) I have enabled monitoring of thread usage based on the scoreboard usage (/usr/sbin/apache2ctl fullstatus) numbers, it prints busy worker thread as 150 and get reset to 0 in next Min when error is observed. is Apache reset all the worker thread when it gets an error as mentioned above?

Thanks in advance for attention on this matter.