Next May wife and I are going to Lake Como next May and would like to go to Switzerland for 4 days flying out of Zurich. I may or may not have a car. Of the 4 nights, we would stay in Zurich the 4th night.
The places I would like to see.
Locarno
Zermatt,
Interlaken -visit to Grinderwald
Lucerne

I might be too ambitious for a 4 day trip..
First, is Zermatt too far out of the way to include as a destination?
Second, from Lake Como can I drive to each destination?
Third -Which of these areas would be best places to stay over 3 nights?
Fourth, if i am taking trains, can I reach all of these destinations?

Definitely too ambitious!

Why not stick to Locarno? Enough to fill many weeks around Locarno, Lugano, Ascona, Bellinzona. Three nights (the 4th in Zurich) is only two full days.

Yes, you can reach all of those destinations by train. Switzerland has the best public transport system in the world as far as I'm concerned.

Yes, I would drop Zermatt. Yes, the Swiss trains are the best in the world. You do not need a car, I would leave it in Zurich. I am unfamiliar with Locarno, but the ride from Lucerne to Interlaken is fabulous. We stayed in both of these cities before continuing down to Zermatt and finally to Montreux.