You can draw anything on Autocad if you have the training and experience. It is far too deep a program to get deeply into without training and experience.
Topography is not dealt with in many of the landscape specific programs. You need a program that does something called TIN to generate contours and then the surfaces on slopes.I don't think you'll get far with 3d topo without shelling out a higher amount of money.
I use Acad 3d companion in an engineering office, but get by with ACAD Lt (~$900) in my landscape architecture office. I don't do 3d very often, but Sketchup is what I use when I do. I only use the free version. I make a jpeg out of my acad plan and drop it in as a floor in sketchup. I scale it so that it is roughly accurate and then draw over it and extrude the surfaces. You can draw with dimensions to be accurate. You could easily draw contours and extrude them (like a foam core model). Sketchup Pro does do terrain, but it will require importing that TIN that I mentioned earlier, if I'm not mistaken.
It is not at all difficult to calculate walls from a 2d plan if you have contours and proposed top and bottom of wall spot elevations. It is pretty easy to draw a cross section of the face of wall showing all you need above and below finished grade. You'll pretty much have to do that to generate the information to input into a 3d drawing anyway. I do this all the time in a civil engineering office on all kinds of sites from residences to larger commercial projects. It does not have to be made over complicated.