Its a myth that Scots are that tight, probably spread by Yorkshiremen
A mac mini would be a much better fit, and to save pennies you could get a new one from the Apple refurb store - you save money and still get a full warranty.
Check out John Lewis as well, they often have sales and last time I looked they offered 2 year warranty. There's also ebay.
As for using the screen, it can be done but you would have to purchase a cable and some software to use the G4 as a screen.
Mid size lcd monitors are pretty inexpensive, so I would use the money you have saved from buying from the refurb store to get a flat screen monitor.
There is only an mini server on the refurb store at the mo, but keep an eye on there if you want a new mac, but make a saving
Refurbished Mac - Apple Store (UK)