stock sport black z, what should i do first?

DLSTR

You must ask yourself what deficiency(s), are you trying to address. Sound/exhaust note? Ride quality/performance for the track. Interior noise issues? Hows the oil temp for you as you drive normally/spirited?

You should tell us what you do with it beyond driving it normally. If you are just enjoying it as is, ie, no track or autocross then stock is probably good. Its faster than the law allows from the get go. It corners beyond the average driver and is a more than respectable and capable sportscar.

Im in Germany. Speed is life. I have ZERO mods but an oil cooler from Z1 motorsports. In this country Im not getting pushed around the Autobahn much unless it has much more power. Im stock.

Honestly the best thing I did was getting MICHELIN Pilot Super Sports. It changes the car in the most wonderful way. That should be your first change if you do any at all.