Most of the time I start with 10 million for my clients.
Definitely just common, to start. Even if you can anticipate that preferred shares will be required (e.g., VC investment), there's no way that you can know today exactly which preferences will be appropriate.
Whether to have par value, and what it should be, depends on the state of formation.
For more details about the foregoing brief answers, please see How Many Shares Should My Corporation Authorize and Issue?.
Disclaimer: This post does not constitute legal advice and does not establish an attorney-client relationship.