I had a couple of these... a 240D just like yours and a 300D with 2x the hp!
Get yourself a valve cover gasket-- the old one will be dry and crunchy. Adjust the valves. You'll need 2x 14mm wrenches, one probably ground a little thinner on the open end. Lots of power and smoothness is usually found by doing this. When the VC is off, put a wrench on the crank and check for timing chain slop. Changing both fuel filters is often-required maintenance. The oil filter is a treat, just wait until you see this contraption. I ran Mag-1 5w40 and the turbo was faster to spool up vs 15w40 but still got 1.5 Bar of pressure at hot idle. You have no turbo, of course, but could still find use in the premium oil if you choose.
That battery looks a little small, so when its replacement comes check to see what the correct one is.
The odometers break all the time on these-- there's a chance if you run a Carfax, you'll cry. But the condition of the car is what matters.
The brakes were a hot mess for me. 240d had a sticky pad that was mechanically hung up on its pins due to rust. Just had to file down the high spots. 300d had a bad master cylinder that wouldn't let fluid back up, so it was dragging the brakes slightly. Cooked both front calipers. Hoses were $4 on rock auto last time I checked, a good maintenance item. When they fail, they tend to boil fluid and you lose pedal.
My seat had a broken spring, so I stuffed a pool noodle in there.
The power window switches are rebuildable at home so you can clean the contacts. Just watch the springs and bb's inside-- they fly off. In a pinch you can swap driver and passenger sides, like to get a window up that's stuck down in the rain. Edit, you have crank windows. Sweet!
The steering box will be loose-- they all are-- they tighten by turning the big bolt on the box counter-intuitively counter-clockwise. There is only a limited amount of CCW available before you're just grinding the box to dust inside-- but it'll feel tighter then!