I'm doing a 3" lift with long arms, can I install the springs and shocks without replacing the arms straight away or should I wait until I've had the new arms installed?

 

You can do that no problem

 

Awesome, looks like I have work to do then :p

 

3" lift without control arm adjustment may throw your caster off. Not a biggie, you might notice the difference in steering.

 

I had a 3.5" lift for a few years without adjustable arms. I had bump steer but no death wobble. It's doable but your geometry will be off.

 

Finished earlier today, just went out with a friend and we noticed the rear left(driver side) sags about an inch, is this a fault with the springs or do the have to settle? Also I noticed the steering feels kinda off, almost jerky, we've straightened the steering wheel and centred the wheels, is this an alignment issue or a problem with the stabiliser.

 

Are your axles centered ? (Track bars)
Sway bar links longer ?

You may be feeling a little bit of bumpsteer. Depending on the final ride height a track bar if not installed might help.

 

Axles are centred as best as we could do on the driveway.
The kit I'm using is the teraflex per-runner kit so it came with all those goodies, I've got to get all the control arm mounts cut out and the new mounts welded in hopefully this week, I'm thinking I might handball it to the workshop I'm taking it to.
Google says an alignment should clear that up. Stressing heaps about it - thinking I've done something wrong haha

 

Steering is gonna be jerky because it changer the caster.
With the lift and stock control arms its going to rotate the knuckles.
I ran a 4.5 lift with stock arms for a bit and you could change lanes in a second if not paying attention!
The adjustable arms will correct that.
Not sure about the sagging side. Is the right side spring seated correctly?