If you have your meta tags created then don't worry about this issue of static vs dynamic and SEO. You should never stop improving your website just because you fear the SEO monster! There are soooooo many other ways to promote and market your website; SEO is but only method.
Yes you will need a database on the backend (server side) to have your dynamic website. How you go about that is another question. Hosting providers usually offer a lot of free applications that may suit your needs. You mentioned adding products so this sounds like a shopping cart solution perhaps?
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