Hmm.
How many miles?
What's its history? Did it come from Canada or straight from Japan?
Where do you live?
"common upgrades" - depends. Some people want to turbo their 3Bs right away. I daily drove my BJ73 for 100,000 km and never wanted for power except on the odd trip where I hauled my skidoos behind on an aluminum trailer. It handled hauling fine - just was slower. Some people will put on taller tires to go a bit faster. Some people will convert to LHD but I don't understand that. Some people will put on sliders and ditch the front porch bumper for an ARB. Some people will add bigger lifts. If you live where it's cold, I highly recommend a Webasto. I ran one in my 73 and now have it in my 77. It's all about what you want and what you need.
Cruisin' Offroad
http://www.cruisinoffroad.com/ is a great source if you don't want to create your own armour. I know Amaurer outfitted my old BJ73 shortly after he and K adopted him from me with stuff from there. Great shop.
I am a junkie for old school and OEM stuff. I ran the PTO porch bumper and always had a bench for multiple butts when we stopped for lunch. If you plan to wheel it that may interfere with your front departure angle. Stick on a bigger lift if you want. I liked the reliability of the PTO winch. That being said, carry an extra shear pin (or 3) as a fail safe. If you need a replacement winch cover let me know - I'll be sewing up a batch of them in the next few months. That being said... I don't run a PTO winch on my BJ71 DD these days. So, again, it's about personal preference and intended use.
Common trouble spots - keep the rear wheel ledge free of mud. They have a tendency to collect mud and rust there. I used to scoop out a lot of muck from there every car wash. Use a diesel fuel additive as preventative maintenance for your rotary pump. A lot of people will complain about them but I found my 73 had a bit more oomph than the regular 3Bs.
As far as diesels go - familiarize yourself with the diesel section on here and do some research. You can't beat the fuel mileage you'll get offroad that's for sure.
Post up some more details so others can chime in.
Good luck.