I have taken the liberty of re-pasting SOME of your post.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~#
"a brand spanking new Mesh system with a super fast AMD 64 3500, 1 GB of PC3200 RAM, 200GB of space and a flat screen.
Its a big job and I am not sure where to start and it coming on the 12th Oct. - but I know from past experience that I am bound to get it the wrong way round and then either have to reconfigure, have too small partitions or have a slow machine.
What do I do first? You provide lots of advice on what to buy, what not to buy and then how to upgrade it later but what about a spanking new system straight out of the box."
~~~~~~~~~~~~~~~~~~~~~~~~ It really is up to you! Your box and your pleasure to set up as you want based on past experience.
I would chop that 200Gb into several partitions. In principle, one large enough for the OS and major applications to work properly. Then another for fundamental data - letters - financial and so on.
You are keen on digital photography and might have a large partition exclusively for picture video or sound files.
The point I make is for the all important working system to have enough room, but not so huge that it becomes slow to back up and restore.