1)"As often as possible"
2) Yes exactly, you take the share url and define to whom this link should be available to. For me it was "to all people who has the link"
The only problem with Google spreadsheet , and I hope they will correct it soon, is that it dosen't provide a "cell lock" feature, wich is very annoying. You have to be very careful not to delete or move the headers accidentently.
Hope it was helpful.