“Are whitening toothpastes safe for enamel?”

Generally speaking, Yes, whitening toothpastes are safe for the enamel. I would look for one that has the ADA seal of approvalbecause they have been tested to be sure they are not too abrasive and won't wear away your enamel.  My recent search showsthat 65 brands have the ADA seal. Keep in mind that they have been tested for safety, not whitening ability.  All toothpastes canmake the claim to be whitening because this is a cosmetic claim and does not have to have evidence to support any whitening effect.Simply brushing with water can remove stains from the teeth and make them whiter.  

Yes..as long as you don't brush excessively..twice a day is good

Whitening toothpastes can be very abrasive and long term use can have a negative effect on your enamel. It is important to read the label on the toothpastes you are considering. Some of the whitening toothpastes are meant to be used for a short period of time and will state the instructions on the label. If you have dental restorations on any of your front teeth your dentist may advise you not to use whitening toothpastes or can recommend a specific brand that would best suit your care.

Whitening toothpaste is safe for teeth as the dosage of whitening ingredients are a smaller percentage that professional whitening. If you experience sensitivity, it's a good idea to use a sensitivity toothpaste in addition.

Absolutely