Larry,
I've been using the 3VCS system in all my boats for the past year and a half. It has worked flawlessly. You can use digital or conventional servos and some of my boats have a mix of both. Never a problem. Use the HRS setting if you have all digital servos. If you have any conventional servos in the boat, even in combination with a digital, then use the PPM setting. The conventional analog servos won't tolerate the framerate of the HRS setting and will buzz terribly and burn up in short order.
You only need to buy additional receivers, not more modules, for additional boats. I use the 603FS for the reasons listed in the above posts. All you have to do is link them to the transmitter like Ron J said above. Takes 15 seconds at most. You only have to do it once upon initial install, or if you change transmitters. The receiver is being linked to that particular transmitter during the linking process.
I use 5 cell packs in my boats, partly by choice, and partly because some servos specify a 5 cell pack according to the manufacturer.
Another tip is to go into the transmitter menu and disable any switches or adjusters you will not be using. Some of the switches come from the factory with default functions assigned to them. If you don't disable the ones you're not going to use you may find that suddenly some of your functions may have gotten thrown way out of adjustment and this can be caused by inadvertant finger pressure on some switches or adjusters that were defaulted to rudder dual rate adjustment, throttle ATV, etc.
The system is very easy to set up and use, I'm sure you'll really like it.
