The best settings in Lightroom will depend both on your scanner and on the exact type of film you are processing. I am not very well familiar with Lightroom, but I believe that there are no auto-profiling function in the noise reduction filter. You will have to try out different settings and find out which works better with the specific film. I am not even sure how it works with actual film grain. The intended purpose of the noise reduction filter in Lightroom is to remove digital noise in images from a digital camera, which has quite different characteristics from film grain.
I would assume that you will get much better results with a software or plugin specifically targetting film grain. I have been using 'Neat Image' for more than 15 years now and am very satisfied with the results. It was originally implemented to remove film grain from scanned images, has for a long time in newer versions also supported digital noise, but the newer versions work just as well to remove film grain. You can download a free demo version to thorougly test the results. The only significant restriction of the demo version is that you can only save JPEG files with a fixed quality setting.