1. Can i install a cd-rom unit on the A1200 and if yes can someone give me some ideas ?
yes! of course you can
im not an 1200 user, but, one way would be to get a SCSI interface and attatch an external SCSI drive
2. For the future i am thinking to put that A1200 inside a tower and i wonder for some thinks such us, how can i connect the power supply unit if i remove the motherboard from the original keyboard-box and how can i connect an external keyboard (a pc one or even an A4000 one if it is easier).
if you can find a 4000 keyboard, perhaps it would be easier just to start with a 4000
i hate the 1200 - and a towered one is even worse IMAO
3. If i put finnnaly the A1200 inside a tower can i use 2 ide devices with the onboard controller or this controller supports only one (the hard rive) ?
i think you need an adaptor