I will develop and modify chrome extension

You should target Chrome 8 as a minimum, however the Chrome Web Store was made available to all users in Chrome 9.

All apps go through an automated review process and in some cases, an app will be published without further manual review. There may be some instances in which a manual review will be required before the app is published based on our program policies.

The registration fee helps to prevent fraud in the Chrome Web Store. You need to pay this one-time fee before you can access the Chrome Web Store Developer Dashboard.

If your extensions are currently hosted outside the Chrome Web Store you should migrate them to the Chrome Web Store as soon as possible. The above changes will very soon become effective for all channels on Windows and will become effective for all Mac channels in July 2015.

Users will have their off-store extensions hard-disabled once the enforcement rolls out. However, if the extension is migrated to the Chrome Web Store after the rollout, users will be able to manually enable the migrated extension from extensions settings page (chrome://extensions)

You can restrict access to your extension by limiting its visibility to Trusted Tester or by unlisting the extension from the Chrome Web Store.