Typically dealerships charge 75 to 100% more for parts than parts stores. Parts can also be ordered online. As long as the part is correct for your vehicle you will see little or no difference in performance.
First one should go to a mechanic's school, or apprentice with a mechanic. You would have to learn about such things as an engine block, and where the thermostat is located. You would need jacks to...
The BMW z4 replaced the BMW z3 in late 2002. The BMW z3 was introduced in 1996 shortly after staring in a James Bond movie. Not as easy on the eyes as the z3 but just as nice.