Welcome, diff upgrade and brakes! Depending on how much you want to spend and if you want to street/track your car!
There is a lot of info around when it comes to ca18det conversion and many of smart minds that can help along the way! I say it doesn't hurt to ask!
You'll also get some smart ass's along the way (hi mik) :) and some ppl that will advise you on how "your" car should be, at the end of the day it yours and depending on how far you want to go depends on you!
Also all 1200 utes are manual :)
Waste gate depends on what turbo your running, the pros of external waste gate is being able to hold more boost and it makes the setup more tuneable!
As for oil cooler if you plan on doing track days the ca18det have a small oil problem when hitting corners and fast/slow downs as oil surge can cause bearings to crap them self, I'd go winged sump and be looking into oil cooler if you choose to drive it hard and fast! (thanks for the reminder I gotta find one for my setup) :)
And oil catch can you is an easy fit and also allows you to keep an eye out if you are getting blow by or having any boost related problems causing motor to pressureise
That's my 2 cents