Welcome to the forum eupiteco.
Right-clicking a text frame and selecting "Info" from the menu will show you the paragraph, line, word and character counts for that frame but I don't know how accurate they are or exactly what they count. For example, using 10 paragraphs of sample English text gives 10, 32, 662, 3491 respectively from "Info" but 10, <no count>, 662, 3482 in the Story Editor. Different character counts but I don't know why.
Any figures in braces (from Info) are - as far as I can tell - the amount of text that cannot be shown, normally because the frame isn't large enough to hold all of the text.
Getting back to your specific needs, as far as I know, you cannot find out these metrics from a selection.