This depends, of course, on what software you are running. On my system
Xorg uses roughly 100 MB each. A web browser, such as Firefox or Chromium, will use a lot more.
As far as I am aware, we (the contributors) do not knowingly collect telemetry and/or personal data from end user systems at this time, no. Nor has it been done, as far as I can remember. This excludes services/features provided by upstream software, such as
core/drkonqi, the KDE crash handler, and the corresponding such in e.g. Firefox and Chromium.
At the time of writing this reply, the reply I wrote in What type of release model does Chakra use? is outdated. Originally (you can read a brief history of Chakra here, this may have been chosen to provide some manner of stability on the assumption that the latest stable releases from upstream would more often than not cause issues for the end users. Currently, there is no clear definition of what is rolling or periodical, nor are there any schedules. This may change.