Can we select multiple calendars?
Not at present. You can currently only have one selected calendar; this might change in a future release.
Can we upload our own calendars?
Yes and we expect many users will. You can add as many calendars as you wish so that each user has the right holiday selection and is using the appropriate calendar for his/her region. Note that you dont upload your calendars: you register them through configuration,
Can we use different calendars for different items? e.g. for some rows I might want to use a different calendar than in others.
Not currently but this is a feature that will be form part of a forthcoming release. Similar to the Plus / Minus function you will be able to define a default calendar for the grid but also different calendars to use based on other cells in the row; you will create a Query which will define which calendar to use on a case by case basis.