Hi Klord, and welcome to MySwissAlps!
>> early September... 6 nights in Wengen, then traveling to Varenna Italy... travel from Wengen to Lugano via Goschenen leaving Wengen on September 11 at 7am that connects with Post bus 162 in Meringen then connects back to a train in Goschenen. I believe this bus route goes over the Susten path.
Yes, PostBus route 162 does go from Meiringen over the Susten Pass and you can get off at Göschenen railway station. (You also have a 16 minute break near the top of the pass at Steingletscher, where you change to the Andermatt bus.)
>> Do we need to reserve the post bus ahead of time?
>> Is this route a good option? We would love to hear from anyone who has taken this route.. It appears the scenery would be beautiful.
The scenery is indeed beautiful. I have travelled over the Susten Pass as part of the "Vierpässefahrt" (Four Passes Trip), a round trip on the PostBus from Meiringen. You can see my photos of this section of the trip on the following page:
>> When we connect to the train in Goschenen, is this an easy connection from bus to train?
It should be. The PostBus stops outside Göschenen railway station. Just make sure you remind the driver that you need to get your luggage out from the luggage compartment under the bus.
>> Will this be a scenic portion of the Gotthard route on the regional trains or will we miss the best part of the route that starts in Flulen?
Both routes are scenic, but the Susten Pass trip is far more dramatic.
>> Our other options are all train connections to Lugano by going back to Lucerne and we thought it would be good to experience a different route.
You could also go via Domodossola, but it would take longer.
As you are spending 6 nights in Wengen, another option would be to spend one of those days doing the "Vierpässefahrt" (Four Passes Trip) as a roundtrip from Meiringen, without luggage. Reservations are highly recommended and can be made online: