I'm pretty sure that only the first is a simple question.

There is a program in the marketplace called INJ builder I think

#2 is far from a simple question.

You need a modeling program.  There are quite a few of them - ranging in price from free to thousands.
Wings3D is free (do a google search) and lots of people like it.  I'm really liking Hexagon and Carrara right now, neither is free.

So in order to create any of the stuff you mentioned, you learn how to use the modeling program of your choice and create those things inside it.  There is QUITE ALOT of learning involved in the process - but it's usually best to start at the beginning and work to the end ; )
UV mapper is a good program to get also, the pro version is nice I hear but I only have the free version.  After modeling you then want to make a map for it so you can give it nice textures.

All in all if you want to model stuff to use in poser you want to learn
Modeling
mapping
rigging
Morph managing (I don't know anything about this yet)
decide if it will be conforming or dynamic (each has thier own set of complicated stuff to learn I imagine)
UV mapping.
grouping (learned about this the hard way ie too late = )

get some good links to tutorials and get settled in because you'll be learning for a while.

Good luck to you!

I am:  aka Velocity3d