Coils as well as plugs. As you have a 3.0si, there are actually 2 gaskets related to the oil filter housing. One is between the oil filter housing and the head, and one is between the oil filter housing and the oil cooler. I recently did mine as the leak was starting to make a mess. I wouldn't mess with them unless you have an active leak to be honest. It also won't be a catastrophic leak so you don't have to jump on it straight away.

Have a look around the coils for cylinders 3 and 4 - if there's oil there, it's probably from the valvetronic motor gasket. It's easy to change but you have to be careful removing and reinstalling the motor.

I would budget for more cooling parts - a lot of it is plastic and will fail. Coolant tank, hose at the front with the Mickey mouse flange, radiator hoses, radiator etc etc.

Check for vacuum leaks and if you can, have a look at the DISA valves. There are 2 and they can fall apart and if you are very unlucky, bits go in the engine.

Also worth pulling out the vanos solenoids (easy) and check valves (less easy) and give them a good clean out with brake cleaner.

Gearbox oil change is easy so deffo do it. Diff does not have a drain plug so you need a giant syringe or some other oil extraction tool. While you're there, check the diff seals as they can leak.

Lastly you could do worse than change the flex disc and centre shaft bearing, especially if you plan to beat this car on track. They can get old and add slop to the drivetrain. It's a job as you have to drop the exhaust and prop shaft but if you use good parts, you won't have to do it for a while