Speaking as a caller - yes, definitely amplify the caller!

Also, make sure that it's very clear which musicians are leading the band. This might sound obvious, but one of the disadvantages of larger bands is that it's much harder to adapt to the speed of the dancers, or to anything else unforseen - it's a nightmare if, for example, the fiddles can all see that the caller wants them to speed up a bit but the guitars know that their job is to keep things steady...

I'm not sure about your definition of e-ceilidh - my understanding/experience is that it doesn't necessarily have to be loud (although I agree that it often is), and it certainly doesn't have to be fast. The music is often played more slowly than, for example, Irish or American contra dance, to allow time for more bouncy stepping.