I have been using Carla for stage performances for at least a couple of years..
I set up my Carla session to include a internal Midi-filter
and route the 16 midi channels to different plugins.
My standard session includes SetBfree, Pianoteq, various U-He synths and some sfz libraries. I usually use keyboards where changing midi channel is easy to do.
Last gig I had, an additional keyboard player was plaing with us and I hocked his master keyboard to an empty usb-slot and connected him to one of my plugins. Everything worked so well.
My problem is more that Carla is super flexible, the plugins are too and my very configurable midi keyboard (one of them) Nectar Panorama P6 is too. This gives me way too many options and ways to improve the setup.
/Anders