Hi,
You'll need a Kickstart 1.0, 1.1, 1.2 or 1.3 disk (1.3 is the most recent for this machine) and a corresponding Workbench disk to bring up the Amiga 1000's GUI.
The OS cannot be bought any more, other than as part of an emulation package called
Amiga Forever. This contains the files you'll need to get your real A1000 back up and running. However, do you have access to another Amiga? The problem you'll have if you only have access to a PC is that the PC cannot write out disks in the Amiga's disk format without the aid of a special disk controller.
As for the specs of this machine, just Google for it! The contents of the original Commodore specification sheet can be found
here.
Finally, what's your location? Perhaps an Amiga user near you might be able to send the appropriate disks to you if you ask nicely!
- Ali