It would help if you were more specific about just which 'cache' you're referring to. There's the system cache that's relative just to the Android operating system on your phone, and there are multiple app caches unique to each app. For the system cache, you need to be running in your phone's Recovery Mode and select the 'wipe cache partition' option. With a Moto E5 Plus you need to boot up into Fastboot Mode which then allows you to go into Recovery Mode, see instructions here:
https://www.hardreset.info/devices/motorola/motorola-moto-e5-plus/recovery-mode/
But if you want to just want to wipe a specific app's cache, go into your Settings >> Apps menu, find and open the entry for that app, and then look for the 'Clear cache' option. To wipe all the app caches together, you can do this in the Settings >> Storage >> Internal storage menu.
But generally, you should just leave the caches as is. You delete them when you're having a problem with some specific operating system function or with an individual app. Wiping them just as some kind of maintenance task is misguided and not productive at all.
The system cache is there for a reason, the operating system uses it not just occasionally but continuously. And apps need their own caches to function. When you delete them, the OS has to rebuild its cache and each time you use an app when it can't find its now missing cache it has to rebuild it. So wiping caches for no reason has no significance nor benefit, and in reality only makes you phone work that much harder to replace what you've deleted.
There are a number of apps in the Play Store that claim to 'magically' increase storage space and optimize system resources -- some of them are just bulls****. They present you with cutesy graphics deleting things like app caches, an illusion that this is going to make your phone work more efficiently but is actually just doing the exact opposite.
As for closing apps that are running in the background, why? You're better off letting Android's memory management handle things than trying to micro-manage things yourself manually. Instead of going through the bother of closing apps all the time, go into your Settings >> Battery menu and set up your battery optimization settings so Android is taking care of what apps are running in the background. Also, in your Settings >> Apps menu, if you go into each app's entry there are a lot of options regarding notifications and permissions you can set in accordance to your particular needs. It may seem like a hassle to just set your phone up the way you want but it's a long term investment of your time, plus digging through your Settings menu makes you more aware of the various functions you have control over with your phone.
