Reservations in Switzerland and not necessary (except for the few special panoramic expresses). There are always enough seats available, almost nobody books a seat and IMO reservations in Switzerland are a waste of money.

6 minutes in Visp is enough time.

There is no need to reserve on Swiss domestic trains, while it is possible on some it is not necessary and most passengers do not reserve.

Swiss train timetables are designed around connections and are run exceptionally punctually, if a connection is listed then it is expected that it will be used.

You can always ask the train staff, they will be able to tell you where to best leave the train and the layout of the connection to make it as easy as possible.

for connections you can check Swiss Railways website sbb.ch, they can provide the best informations for your trip.

And even if there is a mishap on train 1-can happen-very rarely-then not much is lost-all trains on all lines run at least ev hour-on major lines even more-so then you just take the next one. IF you want to use your pass to full use you can also take more zig-zag roundabout routes that include more scenic lines where the Swiss are so famous for. It will then take longer of course.

You are not going to the back of beyond behind wagga-wagga high up in dingo-county.