For games running off floppy disks, there are many games that will not work on the 1200. The 1200 can run almost all games, but it has to be WHDLoad versions which run off the HDD. To make that work properly, you need an accelerator and a HDD.
You can get CD-ROM interfaces for both the 1200 and the 500, however if you just want games, I do not see much point in having a CD-ROM drive. Only reason could be if you want to run CD32 games on the 1200 (although many of them can also be found in WHDLoad versions).