I have also owned an 03 147 jtd, 1st purchased with 77k on the clock.
My drive to work is country roads and the clutch is in constant use, and is lasting well as its the original.
As I understand it, because your car does a lot of motorway miles the clutch should be fine.
My only expense has been the brakes, which is fine if you can fit them yourself like I do, but the garages tend to charge a lot in my view for changing these.
A good site for service costs is www.alfaworkshop.co.uk
Use this to base your budget on. (the site also has a buyers guide that points out any problems in the range)
I personally always add an iterim flush, oil and filter change between services just to keep the engine in tip top condition and prevent any
unecessary engine wear. (I feel this is a must)
Not sure if yours has leather, if it does then I would also recomend
Liquid leather cleaner and restorer. As your car is over 3 years old, its a perfect time to protect the leather for another few years to prevent cracking ..etc
You've got a great car, if looked after, its not expensive to keep her well.
Hope this helps.