1) No, unless you use a custom built map (in galaxy forge) that is set to fixed start positions

2) While ships will sometimes move in the z-axis (which is more annoying than anything else) its currently not something you can do with building structures AFAIK. Also I'm pretty sure changing this would be difficult if not impossible given the way the game determines structure placement eligibility (ie whether a strucutre is in the way of building something else).

You have to manually bind the Z-axis function to a key (for rebinding a key, go to the game's main menu and head over to the Controls panel). Hold alt when placing a structure (or assigning ship movement), then press the key you used for the Z-axis and use the scrollwheel of your mouse to change the position of the structure in the gravity well. Once you found the desired spot, just  press the left mouse button like you would normally to give the order.

I have tried the Z-axis movement but it does not work. First i mapped the Z-axis to the Z key.I have tried it with the build of a Gauss defense platform. Just as Teun-A-Roonius explained Z-axis mapped key, holding alt, scrollwheel just zooms in  and out...where do i go wrong?

Yeah, I gave it a shot last night and it didn't work for me either. No big loss though, I cant see it being terribly useful except for aesthetic satisfaction and for that I'd rather zoom in on a battle