No, this has no influence on your profile and is not visible to other clients.

Yes, you must state all Textbroker earnings (regardless of the amount) in your tax return. Please contact a licensed tax advisor for more information on how to report your income.

No! All texts must be a unique work and can not, in whole or in part, coincide with any published material. This goes for your own work as well as third party resources.
You may use quotes if necessary, if referenced and attributed appropriately. Furthermore, only short passages of a text may be quoted. An adoption of several sentences or even an entire passage is prohibited. Also, you should use as many sources as possible for your article and always compose copy in your own words to guarantee a unique style.
Please bear in mind the copyright laws as well as our Terms of Service. A violation can lead to serious legal consequences should a client or the owner of a concerning copyright learn of illegal usage of protected material. This also counts for Wikipedia entries.