Simulating gradient of a magnetic field, induced by 1 turn copper wire

Hello,
I come from Germany and I study Biomedical Engineering.
I am very new to COMSOL and using right now a 14 day trial version on my home pc.
I was looking last days through several models of comsol, to trying to get the idea how to simulate different problems.

Now I am trying to simulate my own problem and need a bit help.
First I want to describe my problem, and second aks some questions, and hope somebody could help me out.
So, the description.
I have two identical wire loops placed above each other. The symmetry axis is in between them. The direction of the current on both wire loops is similar, so the resulting gradient of the magnetic field from one wire is amplified by the another wire. Thats the idea. The surrounding material in the region is air, and the material of the wires is copper.
This is only analytical setup, and this not going to be build in a real experiment.

So, now to the questions:
1.Which geometry do I choose? 2D or 3D.
2.How can I define where the axis lies?
3.Do I choose the magnetic fields model setup?

Thank you very much, and greetings from Germany.