Welcome to the club mate I'll try to answer a few Q's for ya
What I would like to know is...what are the running costs/mpg like.
I use mine just for the weekends and the odd evening, I like to go fast (which is why I've got it) and would say mine is about 25 mpgs but normally only doing short runs, much better on long drives though
Are there any known problems with the cars, getting parts etc?
most of the car is the same as the IS so most parts not a prob. tuning parts you can get a fair bit in the uk for performance mods or just import, doesn't look like a prob for you
What benefits over the IS200 (which is cheaper).
more power :D , a uk IS is more refined than an imported RS
What sort of price would I expect to pay for a 1999 with low mileage Z edition with the nice kit on there?
Dunno, I've got the legana kit on my which is a front bumper, TRD skirts (side and rear) this was fitted as standard to some models, earlier ones I believe
What is the tuning potential for these cars? I was thinking of some Advan RGs 18", a set of Tein's, Blitz full exhaust and filter just to liven things up a bit as I may do the odd track day (something else that appeals to me!).
400-500hp at a guess
I'm looking to be running over 200rwhp by the end of the year (fingers crossed) just on a N/A set up
Is the auto, or manual a better purchase...in the auto, is the e-shift like paddle? smooth?
I have a 6 speed MT, the auto is a 5 speed box,
MT 210hp - Auto 200hp as standard
think the Eshift is 2 buttons rather than a padel system
What sort of toys does the car come with absolute standard, apart from A/C...elec windows? elec seats? leather? etc.
there's a few post on the different specs of the RS in this forum so have a good look about,
never really bothered me all I wanted was a RS
hope thats of some help