It's relatively easy in this case. Open task manager> Right click on explorer.exe and choose properties> On the General tab, the Location should be C:\Windows (assuming C:\ is the drive where the OS is installed)
You can also click on the details tab which should identify it as a Microsoft product.
Mine is running at 51k to 52k, so take things you read with a grain of salt.
Usually there will be 2 explorer.exe's if there is an infected one, and the spelling will be slightly different, and it won't be located in the root of Windows. It may show up as being in C:\Windows\explorer\exporer.exe, for instance.
Resource usage will vary by machine. You can get more info using a program like Process Explorer, but it's hard to say exactly what is using resources. If you have windows customizations like shell32.dll enhancements, there will be increased usage.
When in doubt, scan with Malwarebytes, or other antivirus/antispyware applications.