Do the Caps & rotors yourself, they are indeed easy to change out. As to the tensioner, $400 sounds fine.
As to the motor mounts, I think I'd farm that out too, because if they're not done perfectly you could be inviting weird vibrations into your drivetrain.
"If everything seems under control, you're simply not going fast enough" --Mario Andretti
1995 E500 street car
1986 Porsche 944 Turbo S track car