There are only 7 masters and 7 servants.

Taken from the Lunar boards. As of the eps that have aired:

<master>/<servant>/<servant's identity>
Shirou / Saber / ???
Rin / Archer / ???
??? / Lancer / Cuchulainn
Shinji / Rider / ???
Ilya / Berserker / Heracles
??? / Caster / ???
??? / Assassin / Sasaki Kojirou

I believe the series will be 26 eps long.

Saber's Noble Phantasm is supposedly incredibly powerful. I'm not sure she was actually charging it, it looked to me like she just took the sword out of the sheath and was preparing an attack, just as Assassin asked. He was also waiting for her to attack. His identity gives away some characteristics. Sasaki Kojirou would feel slighted if she didn't give it her all (he said as much). His pride would make him want to see if he could take the force of her attack. Just like Kojirou's famous fight with Musashi.