To use standalone cellular the Apple Watch *must* be configured to activate the eSIM as a second device on your iphone’s Calling Plan, and at this time eSIM does not support roaming away fr9m your home network. These two restrictions mean it is probably pointless for you to buy the cellular version. It is not essential to activate cellular, but the cellular version would simply fall back to work like the non cellular version so it would be a waste of money to buy the unusable cellular features.
If you can remain within Bluetooth range of your iPhone, or you work in an office with access to WiFi where you can connect the phone and watch, you might find the GPS only version will work for you. If you are within Bluetooth range the default communication lis linked through your iPhone even if he watch has cellular function, and cellular is only used as the last resort. Please take a look at How to use your Apple Watch without your iPhone nearby - Apple Support for functions available when you move away from Bluetooth range but still within WiFi cover.