Wow. that's a lot of questions in one go. I'm also still learning to model, but I'll chip in anyway with a few tips I have picked up along the way.

 

"What are some of the best safe modeling practices and worst modeling taboos?"

 

Almost everybody approaches modelling problems differently, but in general, quads are good, tri's and n-gons can be problematic. Edge loops (loops of polygons) are your friend. Learn the correct places to put your edge loops and you will be a happy camper. On characters, design the loops to follow the flow of the muscles, so the model will deform and animate well. Start simple, then build complexity. Well placed edge loops will make all the difference.

 

Some modellers break all these 'rules' and still create fantastic models, but learning the rules will help you know when you can and cannot break them.

 

"Any C6 specific modeling protocols or methods that may cause problems in other formats?"

 

If your planning on modelling objects, props, vehicles, buildings or simple charcters then Carrara will be fine. On a personal note though, I have tried many times to create a human model in Carrara 6 pro and I have found it so difficult that I'm not sure if it's possible with Carraras modelling tools alone . By comparison, I bought a copy of Modo and I learnt how to model a reasonable human being in just a couple of days. Carrara is OK, but there are much better dedicated modelling apps out there and it's worthwhile checking out some demo's.

 

This could be just me, but I'd bear that in mind.

 

"Any common practices regarding polygon shapes (triangles, rectangles, etc.), polygon counts, number of edges sharing one vertex, etc.? Techniques to use or avoid?"

 

Quad polygons deform and divide well. Tri and n-gon polygons tend to leave artefacts in the render and don't deform or divide so well. Tri's and n-gons can be used if you place them judiciously on your model (usually tucked away somewhere), but keeping your model in quads will probably give you less headaches.

 

The downside to quads is that you will undoubtedly get poles (a place where more than four edges meet). You will have to learn to deal with these by placing them on your model in areas where they will not cause any artefacts or problems with deformation.

 

Squares divide much better than rectangles, especially when used in an application such as ZBrush. If you imagine dividing a rectangle, you will get four rectangles, so you will need to divide a lot more to get detail than you would if you had evenly sized square polygons.

 

Some people are almost autistic about quads, others are more easy going and some don't let it trouble them at all. The rule being, If it looks good when rendered, divides and deforms well, it's OK. However, keeping your model in quads will most likely do that.

 

"Any hideous shader issues from one format or program to the next?"

 

Procedural textures/materials/shaders will be different in every application, so you will have to adjust them accordingly to suit whatever application will be rendering them.

 

"Any particularly sticky Poser content issues?"

 

I don't use Poser, so I don't know.

 

"What would be the best, most usable format for other programs?"

 

The OBJ format pretty much translates across all worthwhile 3D applications. I'd go with that.

 

 

If you want some really good advice, I think you should check out CGTalk

 

When it comes to modelling (and anything 3D related) the people there really know their stuff. Many of them are professionals who work in the industry.

 

Good luck, and most of all, have fun!