For installing KitKat ROMs on Galaxy Ace, you need to install ClockWorkMod Recovery 6.x. While installing CWM 6.x, most of the users will get a BLUE screen as recovery. If you want to get out from there, you need to reset your phone by flashing stock firmware via Odin.
I Personaly love ClockWorkMod Recovery 18.104.22.168, coz it's stable and also supports RFS, Ext4, Ext3 or Ext2 formatted Custom ROMs. Currently CWM 6.x does not support any stock ROM or stock based RFS custom ROM.
Here's one trick to modify any CM 11 / Android 4.4.x ROM for Galaxy Ace (Cooper) to support installation with CWM 5.x.
It's actually a small change in tag of updater-script. The new CWM 6.x uses 'set_metadata' tag for setting permissions. While old CWM 5.x uses 'set_perm' tag for that. I just simply changed that tag. So it may be installed with CWM 5.x.
Step:1 - Download this zip file. [CM 11] With CWM.5.x.zip (Dev-Host, 255 KB)
Step:2 - Download the ROM zip file, you wish to install.
Step:3 - Open ROM zip file with WinRAR/7Zip.
Step:4 - Extract 'boot.img' & 'system'-Folder to current folder.
Step:5 - Open '[CM 11] With CWM.5.x.zip' with WinRAR/7Zip.
Step:6 - Select and Drag the 'boot.img' & 'system'-Folder to WinRAR/7Zip window.
Step:7 - Wait until the files are added to the new ROM zip file.
Step:8 - Close the Zip file.
Step:9 - Rename it as you wish.
Step:10 - Copy the new ROM zip file to SD Card, and install with CWM 5.x
Warning: Take a Nandroid backup of your current rom, before doing this....
Credits: xsalahx's thread post for this idea.