Just bought my 1st Patrol 3.0 Di - any advice on what the garage should check?

Hi - I'm new and have just bought my first Patrol GR 3.0Di (2000). Got it for quite good money, but there are some things that need doing to it:
tracking & balance (steering wheel juddering at certain speeds)
brake overhaul (rural & farm runaround for my wife, daughter and (soon to be) son ) so want them 100%.

It's off to the garage tomorrow and I'd like to get them to check out some other bits (figure it's worth making sure that they're right now):
gear box and diff oils
front hub lube (they're autos)

Is there anything else that I should get them to check? How do I tell if the engine has the timing chain or belt? Have heard that the tensioner on the belt can go, so is it worth changing that as a preventative measure? Engine fluids are ok.

Also, the front hubs on the car had been set to "lock" - I've since changed them to auto and backed the vehicle up until I think I've heard them click out. Are they likely to have been damaged at all as a result of being locked whilst in normal road use? Or do they just cause you to use more fuel?

Bit of history on the vehicle - CAT C repair (drivers and rear door damaged and replaced - no sign of any damage underneath the pan). No book with the truck. clock says 43K miles, though interior suggests a harder life, but it could just not have been looked after. Suspension and running gear is tight as a drum though - certainly doesn't look as if it's been to the moon and back.

Final question - on performance - nothing low down the revs in higher than 3rd, then turbo kicks in at about 2750rpm (if you can get it there...). Is this performance normal? Anybody fitted a diesel tuning box to one of these? Do they improve performance & mpg?

Sorry - lots of questions can anybody offer advice?
Thanks