I have a 05 model Disco3, it's sitting on 109k but is a diesel being as i live in the UK.
The basic mechanical parts are the same though.
By 100k it should have had the following changed for new parts.
Front wishbones, if it knocks going over a bump, then that's the ball joints needing changed, if it knocks if you hit the brakes, then the inner wishbone bushes are shot. Chances are the bolts are siezed in place, (mine were and many UK ones are, due to the salt etc we put on the roads every winter ) so they need cut out and new bolts fitted with the new wishbones.
A wheel alignment is needed after this, which requires the car to be told to go into "tight tolerance mode" then the wheel alignment can be done.
The ARB bushes will likely need to be changed, this can be done on the driveway if you want to. It's a basic job that takes an hour or so for the fronts and similar for the back.
The gearbox oil and diff oils are recommended to get changed every 100k, the gearbox should be done every 70k if used for regular towing.
The air suspension is reliable if looked after, it has covers to protect the bags from damage so a tear in one is from abuse and being a twat with it. There is a new style compressor as used on the Disco4/LR4, this can be fitted to the 3, but needs a software change to run properly. Height sensors can act up, but a code reader will show up what's wrong and then you can swap out the broken part.
For off roading, how you use it will determine the level of prep. For light use, a decent set of tyres and a front guard will be fine. If your wanting to go more into the wild, then plenty of member's here have under body protection, rock sliders etc. Some of the trucks that are on here are superbly turned out and i'm using a few as base ideas for my own.
It will take you most places in comfort and it's on road manners is excellent for a large 4x4.
The Disco4 with the 3.0 tdv6 engine has won "What Car's" large towing event for the 4th year running, the old 3 has won it a few times as well. It's regarded as one of the best all round 4x4s on sale in the UK and THE best tower. Take that as you wish but the car mag has been running for decades and is well regarded as a non bull**** mag.
Electrics can be fitted in an hour, i fitted mine 2 weeks ago and i use the removable tow bar as i only do light towing. The "heavy duty" LR version is really good, and can be removed with 2 bolts and unlocking the centre part if needed to be taken away to help off roading.
I love mine, it's a fantastic all round car for my needs, the mpg is a bit of a sore point but thats only because it's $9.94 for a UK gallon of diesel, so a full tank here is $185. I bet you US folks don't pay that.