Default [Q] Android 4.3 rooting on GTI 9305 on Three UK

Greetings,

I own a Galaxy S3 GTI 9305 on the Three UK network. that a while ago got upgraded to Android 4.3. The software update gets on my nerves and has numerous problems (such as no text message bleeps unless you set a text message bleep for someone) and eating battery life like there is no tomorrow unless you hoik the screen brightness down to nothing.

Needless to say, it's driving me up the wall and I want to install a custom ROM.

The phone has been flashed with Odin, and I used the boot recovery p workaround and SuperSU shows up. However, this super paranoid Knox software has a dislike to the SuperSU app and blocks it.

The phone comes up with ClockworkMod recover if you press volume up, menu and power and I have put a custom ROM and the Gapps file on there.

The thing is, will this phone be able to run the custom ROM as normal (on the basis of ClockworkMod being on there and apparently functioning ok) or is there further nasty surprises that will prevent me such as a locked bootloader?

Apologies for possibly asking this question ad nauseum on the basis that it may well have been asked before.