Point scales can vary and should be adjusted to the ability of your players. Game like drills. An important aspect of developing players' confidence in serving during a match is to create serving games at practice. It can be games where servers play against other servers or contests between passers and servers. Hitting can be done from balls tossed by the coach or set by a setter.
Defense can be from hits by the coach or from real hitters.
The more players are involved in the drill, the more game-like the drill is. The harder the score to get, the more pressure the players will feel. And they will get better at handling that pressure if they have been placed in pressure situations at practice. Serve from as far back as possible. This will enable your float servers to hit the ball a little harder hoping to make the ball move as much as possible.