Multisite info

I would like to ask you for a suggestion about a customer request.

My customer want to realize a multilingual web magazine with different WP installed on different subdomain… magazine.com/en/, magazine.com/it/, magazine.com/de/ and so on…

Any site must have its sitemap and an advanced search option. The customer also ask for an “only one” user database. So, which is your suggestion? According to you which of your plugins we have to use to reach the best results