Hi and to the forum.
Running costs depends on how lucky or unlucky you are.
There are electrical components on the 350Z that are mega expensive like ECU, BCM, ABS Module etc.etc. There is no maintenance on these components so it is really down to luck.
Overall, these components aside, the running costs of the Z are very reasonable.
Low mileage with verified service history and no previous panel or paint work is a good start.