Difference between Series 7 and 8

Hi dear owners of watches.

I faced up with the dilemma of which model to buy a 7 or 8 (GPS+cellular). It is time to decide, but a couple of questions still are not clear to me.

1. Is there a difference between models in terms of use as a phone. For example, if I forgot or left my cell phone at home, will I receive calls, sms, can I use the internet or the app without iPhone somewhere closely?

2. Is there a difference between the two when using esim. For example, in my country (A) I have a physical SIM card in my phone and the watch has e sim card, then I go to another country( B) for a long time or often, I change the physical SIM card to the physical one of that country (B) in my phone, can I load esim card of country B into the watch provided that I do not need to use both SIM cards of A and B countries? In the store I was told that this is only possible with the series 8, and I have not found it on the web, so I believe it is possible that either they needed to sell series 8, or they did not understand my question.

Thank you in advance for your reply