Basic maintenance and vigilant inspection of all parts is the key to disco ownership.
What year and mileage is your vehicle?
As mentioned, all fluids need to be changed, flush radiator, brake lines, tranny, etc. Check and replace all vacuum lines and rubber hoses if questionable. These vehicles are 10-20 years old now and rubber/plastic deteriorates even more so in harsh climates. Try to track down leaks (I know you have some) and determine if they need gaskets need replacing. Check suspension bushings, shocks, etc.
Track down a rack on Craigslist.
Give it a 2-3 inch lift and larger tires for immediate increase in trail readiness. Find some sliders and diff guards for protection. Think about beefy front bumper with wench. There are tons of builds on the site. Grab a beer and pad of paper and start reading... Good luck.