How can I get access to the salesforce environment hub?
Do we need to build a managed package first or We have to develop a package on org generated by the environment hub? Will the environment hub be available after a security review ?
Salesforce Environment hub is a general feature that you can request be enabled in any org. As a special warning, though, you should not turn on Environment Hub in your Managed Package Development Organization, as that can create unwanted dependencies. You can have it enabled now simply by submitting a case, or, as part of the ISV ob-boarding process, Partner Support can enable this for you. You can read more about Configuring the Environment Hub in the documentation. You can link any org to an Environment Hub at any time, so there's no requirement to link your Managed Package Development Organization org ahead of time before the security review; you can do it any time you like.