Inna V. Shimanovsky, DMD

It looks like those might be cavities.  Not sure why they seemed to appear overnight.  either way I would recommend for you to see a dentist and this should be fixed easily.  Good luck!

It would totally depend on your insurance policy. However, majority of insurances do cover it as major benefit at 50%. 

You may want to get a second opinion on this tooth. There is a possibility of persistent bacteria in your tooth that may or may not resolve over time. Also, it sounds like there might be a root fracture.   Get an evaluation with a different endodontist. 

This is what I see in your smile:
As you pointed out there is definite color discrepancies between your teeth, your arch appears more narrow making the front teeth stand out more and appear larger.  Your lower front teeth are slanted a bit although, I am not sure how much they show in your normal smile.  
The appearance of your smile overall can be fixed with dental veneers.  You will be able to achieve uniform color, form and overall a pleasant beautiful smile

I believe the main reason that your bonding are breaking is your bite.  It looks like your might be grinding/clenching your teeth and that break up the bond and composite on your teeth.  White speck is minute and could be fixed easily.  

I highly recommend a cleaning.

The curing light touching your tooth is not of a concern at all.