Where do you start?
Do you wanna go with daytrains or Nighttrains?
Do you wanna stay flexible or have a fixed shedule?

This questions should be answered by your self and have in mind you still need reservtions with a Railpass for the Nighttrains.
To have a detailed answer you should share more details.

Hi, Thank you for answering so fast! I’m starting in Zürich. I don’t mind wether it’s day trains or night trains. I would like to go on the 11th March (or a day or max. two days later).

If these are the only trains you will take if might be cheaper to buy normal tickets if you buy them well in advance. But you need to make the calculation yourself. 

Assuming you require a 4 day pass (i.e. 4 travel days within a month) it will cost an adult 194 euro. This allows you to travel on an unlimited number of trains on any 4 days (boarding from 0000 to 2359 CET) within a month of your first day.

Other than some reservation fees (which in Central Europe are very low), there are no extra costs and if trains do not require reservations you can travel on any train that day.

The cost of pre-bought standard tickets are usually cheaper than on the day tickets, but are often non changeable or refundable, so any change of plans will require full price tickets for the alternative trains on top of the loss of the prepurchased ticket.

Only you can make the decision whether any savings on buying tickets rather than a pass are worth the risk and lack of flexibility.