I have braided brake lines on the. GQ and rate them highly. Have had them for 10years.
To be honest though the brakes on a GU from factory are pretty good and an upgrade would be down my list. Certainly at least Bendix Extreme pads all round is a great place to start. The lines and disks could go down the list until needed.
You say you already have New tyres
My list would be something like this.
NADS
Front and rear Recovery Points
Old Man Emu 2" lift
Steal bull bar
Runva xp11 winch
LED light bar
UHF
Chip
Fridge
Drawers