Hi Clio,
For your car I don't know the engine and the millage and if you trust the maintenance book (if any); it looks like an automatic 2.8 !?
Five years ago, when I got my Zed 1996, 1.9 16V, with 138 000 km, everything was factory original on the car; I had the same problems with a very elastic suspension. As I see from photos your road clearance it's standard so all you need is to buy new schock absorbers front and rear. The standard aftermarket set of front/rear coil springs and schock absorbers plus all new related fittings plus the front arms and bushings should be arround 500-600 EUR and you will have a new car for at least 70 000 km! My advice is to not spend on low guard or famous brands as long as the Z3 it's a car for fun and for the soul!
Also I will keep the beautiful star rims you have and of course the 16' tyres; the cost for 17' or 18' tyres it's double!
But I'm concerned by the soft top you have: I noticed that your soft top has a very large arch on the sides and looks as shrinked on! It's possible to have been replaced with an aftermarket with not the right dimensions? Or the mounting was wrong? Because if you look in some other Z3 photos (difficult to find photos with the roof on!), the sides of the soft top are almost covering the arms; in your case you can see the arms half naked......Here you have to manage on the spot because it's difficult to ofer advices from far away.
Also I suggest to make a full Inspection 2, just to be sure that everything it's new for the engine: engine oil and oil filter, brake fluid, antifreeze (it's protecting the inner side of the engine from corrosion, not only from frozen!), gear box oil, gear box oil filter, whiper blades, air filter, fuel filter, belts (if with small cracks) and spark plugs.
It looks scarry but isn't so costly, but you will be safe on the road. The Z3 it's a very safe and reliable car: I'm lovin'it and hope you will do it too!
Best of luck!