When you look for info in the viewfinder, we're talking about the bar under the ground glass:

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Section 13 defaults to showing the number of exposures remaining, but it can be set to other pieces of data:

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In order to change it to display the chosen ISO value, go to Menu -> Custom Settings and change b2: ISO Display to ON.

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There you go, you now have ISO data in the viewfinder.

However, I will warn you against this piece of data specifically. ISO is generally set to the lowest value that you can get away with to provide for an acceptable shutter speed and aperture range. So, you'll set it and won't look at it again until the lighting changes...at which point you'll reset it and then won't look at it again for a bit.

The number of shots left lets you plan ahead, especially if you are photographing at an event (if you get low, change the card in advance of critical moments).

Exposure and Flash compensation values are also likely to change a lot more often and will be useful when needed.

But, at the end of the day, it's your camera and you should set the buttons and information displayed to work for you and your style.

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I am learning to shoot in manual & have had the settings set up on my camera ready to go. However, I can only view the changes to ISO, shutter speed on the live view screen,

Seeing what you're going to get before you push the button requires that the sensor be exposed and able to supply you with a preview...which requires you to be in Live View. As xiota notes in the comments, mirrorless cameras use an electronic viewfinder, which is essentially "live view" through the viewfinder.

SLRs and DSLRS use a mirror to allow for light to go through the lens and up into the viewfinder so that you see exactly what you're going to get before the sensor is exposed.

There are many advantages to this over a mirrorless EVF and vice-versa.

For learning, you don't need live view!.

Learning to shoot means understanding light, how a light meter works, how aperture and shutter speed and ISO work together to create a perfect exposure of a scene. Start by learning how to use your meter and go from there.

If all you do is toggle some settings while in live view until you have something that you like...you really haven't learned anything. Get to the point where you know what the capture will be before you even press the shutter release...then you've mastered the camera.