You could control the players with the external control protocol to launch your channel (or not) and kick of the videos playing. You could probably do this with one channel if you were feeling extra clever, though it may be easier to do it using something external to do the controlling, anything from a iPod Touch to an Android phone to a PC could do it.

Is there any examples with external control in the SDK?

I have another project with 4 different locations, and 10-40 Players at each location, so I will need to build something to control all players at each location.

Will using a PC/Ipod interface let me do this?

Sadly I don't think Roku is the device for your needs, its "external control protocol" is too rudimentary for unattended control of multiplayer setup.

I am simplifying a bit but for your purposes it can do two things:
A) start channel with parameters (so you can show different things on different monitors)
B) send to the player simulated remote control button clicks (so it can navigate inside channel or be used to synchronize start)
This is done per player over tcp/ip (http) connection.

What it does NOT do is give you any feedback of player status (did it start channel yet or is it still loading? which channel is it running? which movie am i watching now? where in my channel is it?).

Also sometimes remote keypresses will get "lost" in the message queue, presumably overflow from feeding too fast. (My experiments of Netflix channel queue navigation show that when fed 50 Fwd commands over 10sec period, with 70% chance at least one of them will be lost)

Things like that can be corrected if human is holding the remote but can really screw things up in unattended setup.

There is an ugly workaround and that is not to use ECP but instead to open a server socket in your channel and expect commands over direct tcp/ip connection. You will have to design your own communication protocol for that.