The crossfade is simply the “automatic” transition when you overlap two clips. The transitions are something you can use to REPLACE the auto-crossfade. I know of NO way of getting back to the auto-crossfade than right-clicking the transition and picking “Crossfade”.
Yes you can. Take a look at my newsletters where I discuss 4 different methods of doing so (I believe it’s vol 1 #9 but I could be a couple of issues off)
By far the EASIEST way to do multi-cam work is by using Excalibur 4.