Hey projectbbc, thanks for your inquiry! Here are some answers:
1) The CGC Plugin Suite currently does not work with VisuStella. It's not for lack of trying, but their plugins are obfuscated due to their policy and they have rejected offers from us in the past to extend to their plugins. We are working on a potential licensing solution with them but that may be a while yet before that is finalized. This is more of a business issue than a programming one so we apologize that we are not able to offer this compatibility at this time.
2) It's your choice! We support both platforms. Both itch and Steam are going to be updated at the same rate by us so as to make sure everyone is on the same version at a given time. Steam has a slight delay as GGG is handling the uploads so it could be off by 1 - 2 weeks but will usually be within the same month. The Steam version gets the expansions bundled in with the Demo Project and any future expansions will be free updates to it. On itch things are more modular and you get to choose what pieces you want and pay for them individually.
Hope that helps, let us know if you have any further questions.
Thanks,
MythAtelier Team