Good evening Vilmantas and welcome to the Events Calendar forum!
Thank you for your interest in our products.
We’ll be glad to answer your questions.
I believe the following article will answer your question perfectly: https://theeventscalendar.com/knowledgebase/can-you-have-multiple-calendars/
Additionally, you will probably very interested in our upcoming big thing that will be perfect for that: http://m.tri.be/19qc
As far as the Muffin builder is concerned, there are no known issues with it at the moment of writing. I guess it all depends on the level of integration you are looking for.
Let me know if that helps.
Have a great day!
Geoff B.