Short answer, yes. .com would always be preferencial but .org/net would be a very close second choice.
Yes.. .org is also a popular domain and its rank well. I have a site running on .org domain and ranks well.
Just like other legitimate domain extensions, there are thousands of good .org sites ranking well. But the point nowadays is, naming sites should have something to do with the site. Like if you choose .org, show proofs your site is truly an organization..
Google does not discriminate between domain extension, until they are country specific extension. For instance, you have a .org domain and are not maintaning the expectations of any authority domain... Google will treat your domain / website like any other ordinary website with an ordinary domain extension.
in general, yes. the main difference between .org and .com is the buying intent of the visitors, which is much lower for .org sites. basically people expect that if they pay money it's a .com. so for any ecommerce site a .com is almost a must, unless you market regionally.
Yes. If .com isn't available go with .org as second best possible choice. Both are TLD's so will work well for SE rankings.
Yes, definitely. If you have a nice domain name and apply SEO correctly on the site, it will definitely rank well.
There is no such a big difference between those .com, .org, .net, etc.., but keep in mid that if you have .org and the .com is ALREADY taken and a LIVE website, then you can potentially lose traffic from direct visitors (that manually write your website address!) Because I am almost sure at least 80% of people will type .com in the end!