Kalendas gets your events from multiple Google Calendars and displays them in your page using a time range.
I don't think so. So far it works with my configuration, but i didn't test it with other. Feedbacks would be appreciated.
Maybe your Google Calendar and your server have a diferent 'timezone' reference. Check this in your WordPress configuration and your Calendar settings.
Yes. Copy the file kalendas.css to your theme folder. The plugin will check for it.
Yes. Copy the file templates/kalendas_event.tpl into your theme directory and edit it as you want.
The calndar must be public for Kalendas to get it. One of the screenshots in the gallery is an infogram explaining how to set a calendar as public and where to get the XML feed.