I was thinking to buy Snippet pro version. I'd like to use custom fields as variable.
I read about dynamic tags, custom fields are not reported. Could it be possible to use those fields? If yes, I could use Snippet as a sort of content construction tool
No, Snippets does not support custom field values via the Dynamic Tags.
However, you could use Articles Anywhere to output custom field values of the current (or any other) article.
regularlabs.com/articlesanywhere