Narai - Shiojiri Station

I'm not an expert when using old trains that don't use IC cards. So I'm quite worried I might mess up and cause inconvenience to others. Would really appreciate some guidance.

I'm going to Narai Station from Shiojiri Station (and will return on the same day). I understand it doesn't accept IC cards. But can I use my JR Pass from Shiojiri Staion to Narai Station, and also when I return from Narai to Shiojiri? Just using my JR Pass?

If yes (that I can use my JR Pass), I know there are no ticket machines in Narai station, do I just simply show my JR Pass ticket when I board the train from Narai (when I go back to Shiojiri)?

Yes, you can use the JR Pass at both Shiojiri and Narai stations. With a JR Pass you can embark/disembark at small unmanned stations and stations without ticket scanning turnstiles without showing/scanning your pass.

Shiojiri is not a small station - you would just use your JR pass at the ticket gates. Narai is smaller, but has a manned window where you would show your pass.
If you have a JR pass, why would you use an IC card when the pass covers the JR train?