I think it really depends on your site's navigation. It's still a good idea to provide Google an XML sitemap. And an HTML for your visitors
Ask yourself what can it hurt? Really nothing so it is good even though your site is going to get crawled relatively fast if you get good links.
Yes its Important it let google read your site easily. Google can not read site if it not submitted to google or linked through other site.
google submits urls without sitemapt. But it is always good and highly recomended to have a sitemap submitted in google webmasters tools
yes there is a need of sitemaps for our websites especially when you want your site articles listed in Google News search and your videos in Google Video search
Please tell me how to make a sitemap? I have heard of them and don't know what they are and how to use them.
I just used a generated one: http://www.xml-sitemaps.com/ and then uploaded that to my server without links to it, and then told google where it was when I submitted my site
Sitemaps only help your visitors to navigate your site better. If your website is built on simplicity culture, you may not need sitemap. The two things that matter to your website is rank and reach. You need these to make money. Even if you try to sell the domain, these two points will be considered above any other.