Hello jptempone
You are quite bold to ask about driving tips on a rail travel forum.
It makes not much sense to go by car from St. Moritz to Zermatt, where there is a direct train that links the two places and is reknown as very scenic. And, you are not allowed to drive to Zermatt, stinky cars were banned there long time ago. As a car driver, you have to park your vehicle at Täsch and go from there by train to Zermatt. Hence, you can skip the car reservation.
You cannot reserve the car train with SBB while the train is operated by BLS train company. Again, you have to drive up the valley to Goppenstein, queue up there to finally go on the car train, waiting times are likely, then, after the train ride, drive down the valley from Kandersteg. As a train passenger you conveniently conquer the mountains at a speed of 200 km/h through the Lötschberg Base Tunnel.
You might want to seek advice in the Trip Advisor’s Switzerland Travel Forum for further advice on car travel in Switzerland. Here we remain at your disposal as train and public transit experts.
Kind regards,
Roland