Arriving from EWR into ZRH you will need to clear passport control but not security. Your flight will most likely arrive at the E gates and your departure will be from the A or B gates. There is a train connecting the E gates to all the other gates, and you clear passport control as you exit this train.
The SEN lounge in E is indeed nicer (IMO) than the one in A. The one in A has the advantage that it will be closer to your connecting flight and it will be past passport control, so you don't need to budget extra time after leaving the lounge for going through passport control. There is also a newish "Alpine Lounge" at A that you can access which is nicer (again, IMO) than the SEN A lounge.
When you get off your flight from EWR you will be in the E terminal area together with other departing passengers. You can walk right to the SEN E lounge if you want. Once you're done in that lounge, or if you decide to skip it, you will follow signs for the A gates, which will direct you to the train. You'll take a short train ride to the other part of the terminal, where the first thing you will encounter is passport control. You will then be able to walk to the Alpine Lounge to hang out there until you need to go to your gate (A or B) for boarding.
As *G you have access to all of the Senator lounges as well as the Alpine Lounge, regardless of whether you get upgraded to Business or end up flying in Economy.
Safe travels!