Article spinning pollutes the Internet with poor quality content. Google's mission is to organize the world's information. Why would Google reward sites that make their job more difficult? I would focus instead on a tactic like guest posting by creating content that people willingly publish and adds value to readers.

One way it could hurt your SEO is if people who link to your site mistakenly link to .com instead of .net which could reduce your inbound links.

Yes, there is some benefit since shorter URLs tend to rank better. It also future-proofs your URL if you change to a different website platform in the future that is not HTML. The file extensions are unnecessary for search engines. If you decide to change it, make sure to 301 redirect the old URLs to the new URLs so that you retain credit for the inbound links pointing to the old URLs. (Source: the book Search Engine Optimization Secrets).

I would personally always avoid the hyphens in your domain if you can. I agree that the usability is a big negative factor. When you tell someone a domain at a networking event you will have to give them extra instructions and hope they remember it. If someone sees your domain offline, like in a newspaper or billboard, they may have difficulty remembering the hyphens. Also, when people are linking to you they may forget to add the hypens or put them in the wrong place and so you could potentially lose links that you have earned. Since people are so used to typing domains with no hyphens, it will make SEO and marketing more difficult in the long run.