New Surf mods

Geez Dave, how long's a piece of string?
First off, you only have a 2.4 engine to work with, so you're limited.
Replace the paper air filter with a Finer Filter from ARB etc.
Fit a 2 1/4 inch MANDREL BENT exhaust.
Ensure your injectors and fuel filter are good (should have been done on importing)
You can increase the boost to around 14 PSI and larger injectors (done via a competent injection service tech.)
Service the vehicle every 5000kms, and replace the oil each time.
Decent shocks and probably new rear springs as I bet you have a 2 inch plus sag in your back end.
A snorkel and long range tank is required for serious long distance travel, as you will only get around 450 -500 kms max from your vehicle on the highway, let alone hard 4 x 4 use.
Join your local 4 x 4 club to get hands on guided help and experience.
Purchase a recovery kit from ARB, and you will benifit from fitting a set of rear draws, storage as the more serious you get, the less space you have.
This is about $4000 - $5000 Aussie shekels in modifications, so isn't bad at all.
And most importantly, never forget that a 4 x 4 will not get you through every type of terrain, only further bogged or hung up than a conventional vehicle!

Hope this is of help, and go back and read the archives, as there's lot's of interesting info and tips.

Best wishes mate.

Ken.
91 SSR LTD