AngWay Hi Angway, you can load multiple eSIMs onto the device however you can only ever have two active at any one time. This feature is known as Dual SIM Dual Standby. So you can have two number and two data connections at a time/the same time.
As for using sandboxed Google Play Services, these apps are sandboxed as normal user installed apps and cannot do, use or access anything you do not CHOOSE to give them. If you decide to register an account and use all the Google suite of apps with that account, all data you input or use them for can be tagged to that account as normal. Privacy here comes down to you choosing NOT to give them information.
Play Services, Play Store and all the Google apps you install will be able to see ALL the other apps on the same user profile but may not interact with them unless specifically agreed between the apps themselves. This can be for using the standard share dialogue or by apps coded with Google libraries/API etc for things such as Firebase Cloud Messaging. How most apps installed from Play expect to be able to provide push notifications as an example.
You can make use of push notifications without logging into a Play account and simply having sandboxed Play Services present in a user profile alongside the apps you want to receive push notifications for.
If you don't have any apps you wish to use FCM and Google for push and just want to install Play Services to use other Google apps. The best approach would be to isolate them from your daily use user profile (likely the initial Owner one) by placing them all into a secondary user or the Private Space, the latter provides a more seamless and easily accessed approach. Just be mindful that if you're using a VPN each user, work profile and private space instance need a separate VPN connection (meaning in most cases your VPN app needs to be available in them all and each will use a device slot provided by your VPN provider).
If there is anything else or the above needs more clarification let me know.