It depends on the age of the Ulysse that you are looking at...
The entry level was the S model, this has PAS, Elec Front Windows, Central Locking (Remote locking if it still works), Front fogs.
The Top end was the EL, This had the same as the S, but with 6 electric windows, headlamp washers, Climate control, Electric Mirror, Power folds mirrors, ABS, Passenger airbag, half body colored fron bumper, nicer interior, mine has seat back tables, and captain seats (They turn round to face the rear passengers, great for picnics, not that the kids are allowed to eat in the car!).
The Mk1 Ulysse's had a 1.9 TD Diesel engine, it was essentially the samunit as the Peugeot XUD engine that was fitted to 405 and early 406. Very strong, and proven engine.
later mk1 Ulysse's had the JTD Engine. This is the same as the PSA (Peugeot/Citroen) DW10 (HDi) engine. It was available as either an 8v (This is what I have) or a 16v.
There were issues with all these engines;
The XUD had reports of thrown rods, too many to attribute to low oil levels, it seemed to affect the 1997-1999 engines more. Althoguh they all went at prett low mileage, so any such units should have been replaced by now.
The 8v JTD (HDi), these had issues with the high/low pressure pumps; Basically the low pressure (Lift) pump (In the tank) wold break up, and send bits of debris through the high pressure pump stuffing this up too, and into the injectors, mullering those too.
The 16v wasn't without its issues either, some of them where part belt driven, and part chain driven. And he chains would sometimes snap without warning, obviously, this would then mean the pistons inviting the valves down for dinner!
Obviously, I know that there are many good and bad examples of either out there, and a lot depends on the previous owner. The service interval of the Hi units is 12k, but personally, I would do it evert 5k, just to be sure the oil is clean.
I cant advise much on the Mk2 Ulysse'sas mine is a Mk1.
Hope this helps.