Wow! That's a lot of questions.
1. What are mesh objects?
A mesh object would be an object made up of triangles as opposed to a poly object which would be made up of quads. There really is not much difference between an editable mesh and an editable poly other than the massive toolset that is available to you when you're working on an editable poly. The editable mesh tools are rather limited. I always work with editable poly objects.
2. What are patches?
I've never worked with patches but maybe this link will help:
3. I would have gone with autocad architecture but I have limited time to learn and 3ds Max is supposedly easier.
Whoever told you 3DS Max was easier to learn than Autocad Architecture needs to have his head examined. Studio Max is an extremely robust modeling, rendering and animation program. It has one of the steepest learning curves of any 3D app, other than Maya which supposedly is the most difficult to learn.
4. Is the workflow similar in 3ds Max? (specific to what I'm doing, that is)
The workflow is similar in that you typically start with a primitive object and then just inset, extrude, bevel, etc. But Studio Max has a much more powerful toolset than Sketchup. You have a lot of control over your model and lots of tools to simplify your work.
5. If I do not need to tranform anything, can I stick with primitives? Would I be missing out anything if I dont always convert to polys?
If you don't need to transform anything then you don't need to convert to poly's. But if you do need to transform your objects then yes, you do need to convert to editable poly. That's how you access the editing tools. If you don't convert to poly you won't have any editing tools available to you.
6. While we're on the topic, when exactly do you convert to polys?
You convert to poly once you have created the primitive object to the exact size and shape that you desire. Then you convert to poly to access the editing tools.
7. Here's a picture of a Sketchup test render that I did a while ago.
The render you posted can be easily created in Studio Max using just the box primitive objects, converted to editable poly and then stretched and extruded into shape.
Hope that helps.