The only mod I did to my first sierra was 215s. It out drove all my mates and was heaps of fun, I didnt need anything else.
I gave it away when the engine blew and spent way to much money on a few Pajeros and then got another Sierra. Best choice EVAR.
Go to Drive.com.au and setup a customised search that emails you whenever one is availiable in your area private adds and ebay autions all show up. Brisbane has the highest density of sierras I think so that helps.
Get it and give it a
really good service, flush and change ALL the fluids, new plugs filters etc.
Once you've driven it for a bit and have a better idea of the terrain your keen on and whats in your area, think about mods.
Lockit and drive it. Lockers are the new flex
Depending on what your driving choosing a good combo of lockers will do much more for the car than tires or gears.
No Body Lift. Low is the new high.
Bumpstops and a hammer, and a grinder are all that is needed up to 31s, which is a good size for a DD.
Gears
Any tire bigger than a 215 and you should get some transfer case gears. Ratio will depend on tires and terrain.
Rear suspension is the new front suspension.
If you want more comfort and more flex or bigger tires, a RUF (rear up front) conversion is what your after. There are a few ways to do it, I did it the most extreme and engineerable way (gwagon's method).
(Gewagon)Steves writeup for new sierras:
http://www.vic.suzuki4wd.com/forum/view ... ?f=5&t=385
is handy.