Need Help- Travel from Amsterdam to Interlaken.

Welcome to the forum Parth! There are direct trains from Amsterdam to Basel. You'll have to change trains to Interlaken there. Night trains from City Night Line are an option too. All connections, including the international ones, are to be found in the Swiss timetable.

Yes, October is fine. Depending on the exact week(s) in which you'll be visiting, you may see splendid fall forests combined with snow capped mountain tops.

Affordable hotels in Interlaken near railway stations are listed here. You may also like the other tips on a budget stay in Switzerland.

Euros are accepted in most major hotels, restaurants and tourist attractions, but not everywhere, so it's convenient to have some Swiss francs. You can change your money at banks and Swiss railway stations.