How copy translated footnotes from word to Indesign

Is there a way to change footnote numbering? 

It is always starting with 1,2,3, considering each page as new page. 

I wanted to change them to 6,7,8 according to my content on word 

It is not best practice to cut and paste text in ID, especially if it contains footnotes or endnotes.

First, make sure the Word file is clean and well organized, with assigned styles, extra white space stripped out, etc. — just as if you were going to send it to someone for typesetting.

Then import the Word file to a new, empty InDesign document, and check the Show Options box in the Place dialog, and review the styles before completing the import.

That should give you a a clean and complete starting point, even if the formatting needs cleanup all the way through.

Footnotes are not usually a problem in Word imports, at least, not nearly as much as end notes.

What are best practices to translate Indesign files?

That's kind of a big question, and also a bit too late, as I'd say that best practices would have been "export IDML from InDesign and have your translator work on it in their CAT tool." But, since you already have a translated Word document, the place to start would be to File -> Place that document into InDesign, and then format the placed document. That would keep your footnotes, at least.