Train fee 15 CHF is the return ticket, bus 5 CHF is one way. The buses do not operate anymore late in the evening, the last train is at 23:20.
The short piece "Wasserloch" IMHO should be rated UIAA I-II, for sure not III-. With wet conditions (name!) it might be II but regarding your pics the "wasserloch" should have been dry when you visited the peak.
Where did you find the overall rating G5-6? On the main page G4-5 is mentioned and that is what I found in the Rother guidebook; the others do not use this scale.
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