I use Bryce 5.5 a bit, and you do not need to purchase any add-ons to work with the program.
Hopefully, the content pack still comes with it, as this includes many materials to apply to your objects, terrains, and sky. The one thing I do not like about Bryce is that you cannot create an object without assigning a terrain and sky (even if it is gray, black, or white). This presents issues if you want to create say a semi-transparent (translucent) object to use as an icon, a part in a skin, or on a wall - due to the fact that reflections are rendered, and therefore the reflections are based on the assigned terrain and sky. You can export image, and then export an object mask, which will allow you to remove the extra content in the image and leave just the object - but you still have the reflections from the extra content of the original image. I hope they can change this limitation.
If you want to create a wall completely in Bryce, create parts for skins that use the materials created in Bryce (which are limitless) and reflections are not an issue, then you are good to go for fairly cheap. If the orbs, torus's, and space images that you intend to make will not be limited by the transparency issues raised above - it may be worth checking out.
As for the other programs, I do not use them.
I find that I use Photoshop and CorelDRAW as staples, and when I have time, I play around with Bryce. Learning how to create materials, and applying them in the correct fashion is - in my opinion - the hardest part of the learning curve for Bryce. The object creation and understanding the axis positions and origins (both global, and relevant) are fairly easy to grasp, especially for one such as yourself - who has used AutoCAD.
They recently released some updates for the Vue line of 3d software. Although it's more toward scenery, it can accomplish other tasks also. They have entry level software starting for less than $100. You can download demos from their site.
http://www.e-onsoftware.com/
Only danger there is with the 'gee whiz...look at that, wow' production that is a bunch of defaults that everyone has actually seen too many times before....the stuff that gives Bryce such a 'bad' name...
Horrid little proggy...