Any working techniques or examples for a multistep AJAX enabled node form
I think trying to use multistep, ajax and the core node form may be quite tricky. I am not going to say impossible, but I think it would be a lot of work. 

I would think using a custom form and saving the node as you suggest may be easier, what you'll loose with this is the flexibility of having it integrated, so if you add a new field to the node, you will need to change your form.