New Mac Pro with Premier Pro - CPU/GPU utilisation

***Can Premiere Proutilizee all potential 28 cores on the New Mac Pro (or any computer for that manner)? Yes/NO

Fewer, faster cores are usually the better choice for video and motion graphics.  If you think you're going to jump into 3D, then more cores.

***Is it the CPU or the GPU that determines the rendering time and does the term accelerated graphics refer to the gpu supporting the CPU to speed up rendering.

Unless the effects that you're using are GPU accelerated, then it's CPU.  In the Premiere Pro Effects tab, effects that are GPU accelerated have a small icon that indicates this.

***Is it CPU or GPU that determines the exporting time? (ignore external drives, SSD etc etc,)

This is primarily CPU and drive speed (read and write speed are very important); however, if GPU accelerated features are being used, then GPU will be helping out.  If you're doing a lot of H264, that's accelerated via CPU if you're running Intel processors and an up-to-date OS.

***For instant video playback during the editing phase, is this all GPU heavy?

For multiple streams of video, that's drive speed.  Once you get into effects and color correction, you're back to CPU and then GPU.  While doing your audio mix, that's mostly drive speed as well.

***I know ram plays a big deal, but my main focus is cpu and gpu, trying to understand how the CPU and GPU affect video editing performance.

Heck if you can afford 1.5TB or RAM, go for it!  Go with 32GB at least, try for 64GB or 128GB.  Then fewer, faster CPUs.

****Last but not least, if you where to take a hot on perfromance, would you rather have a lower GPU or a slower CPU and why

For video editing, faster CPU, lower GPU.

Something to remember with the new Mac Pro will be the Afterburner card for speeding up Apple ProRes renders.  Of course, the Afterburner card and the GPU can be upgraded later.  Unfortunately, Apple hasn't supported processor upgrades since the G3 and G4 processors.  It was really something to be able to take your againg G3 and for a few hundred bucks swap it out for a G4.

This document is a little dated, but you'll probably find it to be helpful:

http://international.download.nvidia.com/adobe/pdf/adobe-hardware-performance-white-paper.pdf

Those are really good questions. I don't know if a single person can answer all of them perfectly accurately but I'm sure that between a few people you could get all your questions answered.

There may be a difference in the architecture between macs and PC's re: what used to be called " Front Side Bus" and how cores are used ( how many during what operations).

Front-side bus - Wikipedia

There is a 'Hardware' subspace in the PPro forum. Maybe you could copy your mssg here, start a similar thread in the Hardware forum, and 'paste' your text into it ( saves time to paste).  I would eliminate the YES / NO choice... even though you want a concise answer to all your questions.  I don't think yes/no is always a good choice, when 'it depends' is sometimes the correct answer.  But that's just my opinion of course.