I used to have an 3.5 IDE HDD and a 4x CD-rom connected to my A1200 for much of the 1990s without any problems.
Some claim that a buffered interface is needed otherwise you risk damaging your motherboard - however my experience and that of others here suggest it is safe. You will need the IDEfix software (aminet?) to get the CD-rom up and running properly.
I would, however, advise against powering the IDE devices from the IDE connector; ideally you should power the CD and HDD externally. I had mine housed in an old AT tower and powered by its own power supply. Good luck with it - and have fun!
