No need to apologize, we all learn new things from each other all the time. If things are working correctly in Safe Mode then that points to a Play Store app (one that you downloaded & installed that didn't come pre-loaded on the phone) as a possible cause of the problem. When the phone is running in Safe Mode Play Store apps that didn't come pre-installed do not run. That's why Whatsapp doesn't work in Safe Mode, it's a Play Store app that didn't come pre-installed on the phone. When issues like you described don't happen in Safe Mode that normally means an app is causing the problem. You could jump into a full Factory Data Reset (FDR) which resets the phone back to original factory settings, like the day you first turned it on, but you lose ALL personal files, pictures, music, etc. That may be a little drastic at this point. I would recommend uninstalling every app that you ever installed from the Play Store. Be sure and write down user names, passwords, etc for when you do re-install them....if necessary. Then go into Settings > Storage > Cached Data and tap that > Select OK to clear all old cached app data (this will not remove any personal files). Then reboot the phone (turn off & back on). See how it runs for a while. If all is good, slowly start re-installing apps that you need / use often one at a time and see how it runs. if you experience the same issues, you know which app is causing the problem.
