Disclaimer: This is the overly protective going to be very picky version of maintenance to a 200TDI. You can probably scale it back from here.
Unless you do something stupid (AKA, overheat, run water through the system, run misc items through the system, put articles of clothing in the fuel tank, stuff old cell phone cords down the intake, etc) its going to be fine. Become familiar with your local diesel shops for tune ups.
If I was getting an unknown mileage 200TDI, I'd replace the turbo (upgrade would be considered at this time, blowing a turbo is a bad time), clean out the EGR (EGR's get gummed up, nature of the beast), replace all injectors (once again, an opportunity for an upgrade), and replace glow plugs.
Leaking injectors happen and cause all kinds of interesting issues. Also a good set of glow plugs is crucial once the polar vortex/winter typhoon/whatever it is this year hits. The tuning and checking of the timing of the injector pump is what I'd have a shop look at. Buy a workshop manual for the engine and it'll have all the specs in it. Also check the manual on when the injector pump should be checked. Also adjustment of valves.
Flush the radiator. Overheating is a bad time. Inversely, buy a radiator muff for in the winter so the truck will actually heat up. This is nice if your commute is short.
Install an Exhaust Gas temp gauge. If something bad is about to happen, that gauge will tell you. Typically you can push the truck less and the temps go down. That will short term get you home but it is a sign that you need to pick around and make some adjustments.
Speaking of adjustments, be careful when taking it to shops. People be like, "Oh, I'll tune up his injector pump. Murica!" That is fine, but have that done 6 times and all of a sudden, you are seeing some weird stuff because the truck is running rich. This is a bad time.
Replace filters, especially fuel filters on time. If you decide to run biodiesel, it tends to also "clean" out the fuel system. Guess where all that crap ends up in. The fuel filter. I've heard of trucks needing a new fuel filter after one tank of biodiesel, but then good to go after that. So yeah, extra fuel filters is probably a good thing to have on hand.
Old truckers I used to work with swore by adding this stuff to their fuel tanks to get rid of moisture in the system. I'd do more research on that but if they were doing it with similar-era big trucks, then its probably not a bad idea. Water in your fuel system can rust away your injector pump. This is a bad time and a couple bottles of that crap will be cheaper and easier.
Lastly I'd replace the lift pump just for a piece of mind. Also I'd carry a spare lift pump. Once again, this is being overly protective.
If you've played around with series 4 cylinders, you'll feel right at home. Replacing injectors, glow plugs, and turbo are all nut-and-bolt jobs. Nothing too ridiculous. Oh but do wear gloves. Diesel fuel is nasty.
Parts are readily available here in the US. If not, Trevor from Rovahfarm can probably get them for you. If you do replace the injectors, look around for injector rebuilding shops. I've seen places you send your injectors off to and they rebuild them for half cost of new ones. Then you've got a spare set of injectors on hand if needed. Great success.
Other than that, should be good to go. These are very good engines and the above mentioned is pretty much what is done to any mechanically injected diesel engine for "maintenance". Do all of that and that engine should be super awesome and reliable for you. Don't do all of that and most likely, the engine will be super awesome and reliable. But the above will ensure the engine returns good power and start ability.
I hope this helps.
