Buy an A1200 remember the old times and from time to time start the upgrade to tower and finally to PowerPC processors or Buy from the beggining an Amiga 1 system.
A1200/PPC advantages:
* The OS is already out
* Fine for hardware hitting games
* You can start cheaply - a base A1200 for retro stuff
A1 advantages:
* Will run newer things faster when OS4 is out
* No wierd I/O bottlenecks
* The "classsic" Amigas are ten years old and starting to fall apart and have custom hard-to-get parts; the A1 should be more reliable
* Will run Linux well
* Comes with PPC/PCI etc out of the box - no major expansion needed
Oh if you can please inform me the Amiga 1 system as it is right now can play amiga older games/applications for Workbench
The A1 currently runs the UAE Amiga emulator, which should be able to run all those. OS4 will be able to run a lot of older apps, but you will be out of luck for most games - someone will probably port UAE quickly, but it's not quite the same as having native support.
What I'd do first is grab an A1200. They're cheap, expandable and will let you play older games, as well as getting used to the platform. If you like OS4 once it's out then you could consider an A1, but there's no point rushing unless you want a Linux box. I'm following the same route myself (got a slightly expanded A1200 with tons of software monitor etc for £40 (just under 60 Euros).