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We can really only give you informal advice. Be polite. Don't hammer the server with hundreds of requests per second, don't leave it going for hours. Consider whether or not you need to index the whole thing or if you could limit it to something specific.
And if you're sharing the result of your scrape (eg you're setting up your own mirror), make sure you follow the copyright requirements for the content. The site designs are explicitly ⓒ Stack Overflow so copying them without permission is a no-no.