Shutting down iMac or not

Hi there! You can restart your device once a while to free up cache memory. You can shut-down the MacBook incase you aren't going to use it in an immediate future. Apple MacBooks are built to handle Sleep-Wake action efficiently and hence if you are a regular user of the MacBook, you can simply put the MacBook to sleep. Trust this helps!

It's really a personal preference. It will not harm your Mac at all. It is generally a good idea to restart your Mac once in a while to free up any resources that may have been impacted by misbehaving programs and processes.

Personally, I leave my iMac on most of the time and to make sure there are no issues with bad/dirty power, I keep it connected to an Uninterruptible Battery Supply (UPS) to protect my expensive iMac from the dangers associated with dirty power. It is the primary contributor to failures of computers.

I use auto shutdown and auto start up daily. Not a fan leaving any hardware on 24/7 unless required.

In preferences, energy saver and then schedule in the left side box.

My iMac runs 24/7 and is only restarted for system updates.