Custom Recovery can be installed without root.
If you have Samsung Kies running while the phone is connected to PC, chances are high that it interferes with Odin. Disable Kies
Try the following method that makes use of adb commands through a commmad prompt from PC instead of using Odin.
- Download TWRP recovery for S5 Mini from here -> TWRP Recovery
Make sure USB drivers are installed.
- Download 15 sec ADB installer
- Rename the downloaded img file to "recovery.img" and move this to the ADB folder that was downloaded earlier. Make sure you have ADB.exe, fastboot.exe and the recovery.img in the same directory
- Enable developer options and USB Debugging in your device
- Connect the device to PC. Make sure device is detected. If not re-install the correct USB drivers.
- Once device is detected, open a command prompt and change location to the ADB directory. Issue the command "adb devices". This should give your device ID as the output.
Executive the following commands carefully:
"adb reboot bootloader" - the device will reboot in fastboot mode
Once device shows up fast boot screen, type " fastboot devices " and make sure device ID is listed
Type "fastboot flash recovery recovery.img" . this installs the TWRP image into the device. If successful you will see an Okay message in command prompt.
Issue command "fastboot reboot" and wait for device to reboot normally. Once this is done you can try the key combination to boot into recovery. If everything went well you should be greeted with the TWRP recovery instead of the stock Android recovery.
Once this is done. You can root your phone/install the ROM.zip file using the TWRP Recovery
Hope this helps.