1. Objective of 360 degree feedback is to arrive at a wholehearted feedback on somebody's performance. However due to various business reasons including practicality, controversies, usually for performance assessment and compensation planning, 360 feedback alone may not be the criteria. Typically organizations follow Half Yearly or Annual Performance appraisal and 360 feedback, together.
In simple terms, this is a process in which an employee shall be scored against certain attributes by self and a group of respondents (i.e from peer group, from reporting community, to whom employee reports to, internal customers (other functions), external customers.
2. There is no such limit on conducting 360 feedback collection. However by considering the huge effort and cost required, better to follow 'once a year' feedback
3. To start with either you may need to adopt a standard 360 degree feedback system (hope there are number of tools available, today) or yourself prepare the tool kit - i.e attributes, scoring method, rating logic, respondent list, administration plan (manual collection or with the help of software)
4. Making employees to participate in the process without fear is going to be the tough job. However with proper planning, systematic orientation and dedication, this is possible.
Wishing you the very best