Other than the fact that you have the slowest iMac offered by Apple at the time of purchase, 8 GB RAM and a 5400 rpm hard drive, I see nothing in your report that's really damaging. However, you should reboot more frequently, at least every over day.
Time since boot: About 28 days
This will clean out system and application temporary cache and swap files and will help the performance of your Mack.
Now, boot into Safe Mode by booting with the Shift key held down and then reboot normally.
NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files
Also helpful would be to not have any apps loaded at launch via the System/Users & Groups/Login Items preference pane. Instead run those apps only when needed and then close them.
You could speed up the boot time, application and file opening and closing/saving time by using an external SSD to boot and run from. These external SSDs from MacSales.com (OWC) are excellent choices: OWC Envoy Pro EX - USB C or USB.
There's nothing you an do about increasing RAM as it's not upgradeable.