Haste cap...
 

Whats the cap for haste? (worn, spell, song....)

100% at cap, rises at 10 level breakpoints iirc.

Not really sure but I would like to point out that bard haste doesn't really stack with spell haste. Its a common misconception. The other positive effects of the song will take effect but not the haste. Whichever haste is greater will take precedence.

Correct, until velious.

Come velious bards get the Ervaj line which stacks with all other hastes, but doesn't raise the haste cap.