>> what are the differences from first to second class. I'm sure the seat is larger
Yes, seats are a bit roomier and there are usually only 3 seats across the carriage in first class: 2 on one side of the aisle, 1 on the other side. In second class, there are usually 2 seats on each side of the aisle. There tends to be fewer people in 1st class, which can be a bonus in high season.
>> but does it come with meals and drinks?
When meals, snacks and drinks are available, they are available in both first and second class, but not included in the fare for either class.
>> Also looking at connections in towns like Brig or Visp, Spiez and Bern are very tight. Is that a problem?
Not usually, unless you have some physical limitations that slow you down substantially. The transfer at Spiez is usually just from one side of the platform to the other. The timetable will give you the platform numbers on which you will arrive and from which you will depart.
>> Some of the connections are like 6 minutes.
That's not unusual, and is designed to be achievable. When setting standard transfer times, they take into account how far you will need to walk to get to your next connection - it's not random.
>> I can make the reservations separate and then make the connections longer but do I need to do that?
In the Swiss Timetable, you can click on "Advanced search", then scroll down and change the "Duration of transfer" option from "Standard transfer time" to 10, 20 or 30 minutes. Then the timetable will generate a series of connections to get you from start to finish with longer transfer times.
Do this before making any reservations, as reservations are for a specific train and not transferable to another one.