@Sanea well the question is different, however still as a fellow professional i want to provide some inputs.
360 Degree as a method - is actually done for feedback, and even in case if its used for Appraisals - the users i.e. the people who are going to provide feedback have to understand the objective, and the way to provide feedback. Maturity and Understanding of the respondents is essential to ensure that it does not impact the process adversely.
For startups, as I understand, that in the initial phases around 2-3 years, the way team is hired, the vendors managed and the over all work environment is very different from how it would be - once it is matured. So before using a 360 degree as a mode of Appraisals, do a thorough check on the readiness of your organization and respondents. Hope you dont mind this friendly suggestion.