What are the aperture details of my AF-S Nikkor 18-70mm 1:3.5-4.5G DX lens?

Hi. I'm a bit confused about this. I read that if my zoom lens only says something like 1:2.8f, then it can open all the way to an aperture of 2.8f throughout its whole zoom range, and that also means that it would be an expensive zoom lens. But what does it mean when the AF-S Nikkor 18-70mm 1:3.5-4.5G ED DX zoom lens says "1:3.5-4.5G"? What does the 4.5G mean here?

Also, when in Aperture Priority mode using this lens, I can close all the way to f22 if I'm zoomed out to 18mm, and all the way to f29 if I'm zoomed in to 70mm, how are those aperture numbers determined? And what "safe" maximum apertures would you recommend for this lens when photographing landscape and wanting to maximize sharpness?

18-70mm - the focal point of a lens, that means it goes from 18(short) to 70(long).
According to focal lens point your aperture will adjust. In your case: @ 18mm your aperture can be as low as 3:5 but @ 70mm the lowest aperture will be only 4.5

I have that exact same lens. It has a maximum aperture of f/3.5 at 18mm, and slowly gets smaller to f/4.5 at 70mm. The "G" indicates that the lens doesn't have an adjustable aperture ring, and has nothing to do with the f-stop range. This lens was built, and built well, as a kit lens for mid-level Nikon DSLR's. As such, Nikon, like Canon, Pentax, Sony, and others, com promised on the maximum aperture and mechanics to meet a price point. A pro lens like their 17-55mm f/2.8 has huge glass elements, mechanics, and professional build. Lenses like that keep a constant maximum aperture throughout their zoom range.

As for your second question, the zoom changes only the maximum aperture. You can choose anything below f/3.5 and it will stay the same at all focal lengths.

For landscape work, assuming you have a good tripod and lighting, you are free to use any aperture you choose. The smaller the aperture and the wider the focal length, the more depth of field you'll have.

Aperture is a ratio. F/2.8 means the focal length of the lens is 2.8 x the opening diameter of the aperture.

And when you reduce the aperture diameter, the f number becomes larger, as the ratio becomes greater.

In consumer-grade lenses if your aperture is f/2.8, at 100mm, and you zoom to 200mm and the aperture diameter stays the same, the aperture goes to f/5.6 as the new ratio has to change because the focal length changed. Consumer lenses that say 3.5~4.5 man f/3.5 at the minimum focal length, but f/2.5 at the maximum. The aperture diameter does not change, but since the focal length changes, the ratio changes as well.

In pro lenses, the ratio stays the same as the aperture actually enlarges. I'm not sure how that trick is done, but at any rate the lens has to be more complex to do that, so that is why they are more expensive.

Generally most lenses do best at f/8 to f/11. Larger apertures typically are not as sharp due to lens softness, and smaller apertures are not as sharp due to lend diffraction. So f/8 to f/11 is usually the "sweet spot".