The chart components are slightly different than the other components since they are wrappers for eCharts and not f7 components. As I understand it, in the chart widgets, not all of the property values are passed through the expression parser. So there are some places, apparently period is one of them, where you cannot yet use expressions. You will likely have to submit a feature request on the webUI github page to get that resolved.
I’m not sure I fully understand what you’re asking here. There are oh-repeater components which give you limited ability to define and work with arrays with a loop-like architecture.
If you mean to expand an array within a single property expression, then the options are very limited. The expression parser is not a full javascript interpreter so only some common operations and methods are available. With arrays you have access to all the basic js array methods but there is one big caveat: most of those methods (e.g., map) require a function as a parameter and there is no way to define function with the current expression parser setup (there is a function add-on that could be installed. I’ve never asked, but I suspect that the devs are leaving this function add-on out intentionally for both performance and security reasons). That said, any array method that doesn’t require a function (e.g., join) will work in the expressions.