There are plugins available here in the community for all your needs. Just search for it.
To add profile fields:
http://community.elgg.org/pg/plugins/project/385114/developer/jdalsem/profile-manager
It's also possible to add them to the registration page.
For users choosing their own background there is a theme called customstyle but I don't know if it works with the latest releases of Elgg.
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