Personally, I also visit communities such as r/skeptic and also r/conspiracy for interesting discussions.
There are already some c/skeptic community in the fediverse:
Mander seems like a good place for one.
I am not so sure. Skepticism fuels scientific inquiry, and yes, people should be skeptical when discussing science. And this skepticism should show up in every community.
What worries me about a community dedicated to 'being a skeptic' is that, in my experience, this is a space that can easily concentrate polarizing views - about religion, gender identity, politics, who is misinformed and who isn't, conspiracies, etc. These become spaces to debate charged political and social issues, and science is rarely the priority.
I think that we have more than enough polarizing spaces in the internet and in the fediverse, so I really try to make an effort to minimize the volume of polarizing topics in this instance.
It is very rarely a hard 'no' for me. You are of course free to create a skeptic community, and it is possible to create a community that does not fall into the 'traps' I've mentioned. If you choose to that, I would appreciate it if you are at least mindful of the mission of avoiding polarizing spaces and trying to stick to the topics of science and nature.
I suspect that a large number of people are interested in discussing socially relevant and politically charged topics in a skeptics community, and so my recommendation would be to use the communities that I mentioned above.