Autocad, MasterCam and 3d sim's

Hello

I am new to CadCam (well actually just getting back into it after 10
years actually). The questions I need answered are simple for the CNC
guru's among you. I am getting a Taig CNC ready (4 axis), gecko
controllers, and steppers as the drives. My questions are related to
software and design simulations...

In the old days it worked this way..

1) CAD software (in my case Autocad, V2 - V???)
2) Tool path generation
3) CAM / tool path editting
4) Run the build
5) Test / and redesign
6) Go through steps 1 - 5 until it works right

I dont want to do solid model rebuilds.... so...
What I need is a way to do testing in software
before I do the builds....

Question(s)
1) I need software to do 3D mech (ie gearing in 3 dimensions) What
should I use? (Autocad, if so what version? Mastercam is mentioned
alot can I use it?)
2) What software is recommended for the following?
a) CAD
b) CAM
c) G-code conversions
d) CNC builds/milling
3) is there any combo product that will do all of the above(ie
everything before actually milling? The milling added in would be a
bonus)
4)


David