How thick should be the sponge for a swiss roll?
Personally when ever I do Swiss rolls or anything requiring me to roll or manipulate the sponge in any way I'll use a Genoise sponge recipe. It's a bit more effort to make than a bog standard pound cake recipe but worth it. 

While still warm I've managed to roll it anywhere between 2mm thick and 3cm with little or no cracks or splits.

In my opinion the optimum thickness for a full sized Swiss roll is around 1cm thick, but obviously if making canape sized versions you'll be looking more towards the 2mm thickness.