I'm not familiar with FIM myself, so I can't really answer your FIM specific questions. You do not need to have Forefront Identity Manager to use FBA with SharePoint. You can have both windows and FBA users on the same environment.
1) I don't know about FIM specifically, but there is a Change Password page built in for changing an FBA users password. There's also a Password Recovery web part that will reset the users password if they forget it.
2) If you're referring to login pages, then yes - but SharePoint comes with that built in. If you configure both Windows Authentication and Forms Based authentication, when you go to login SharePoint will provide you with a drop down where you can
choose which method to use to authenticate. You will then be redirected to the appropriate page. Alternatively you can set up separate zones to the same web application - so when a user hits the internal URL they get automatically authenticated
with Windows Authentication, and if they hit the external URL they are prompted for their FBA username and password.
3) I'm not sure what kind of policy management features you're referring to. The same SharePoint user rights can be assigned to both to windows and fba users - there's no differentiation between the two in SharePoint.
4) The password policies have to be configured separately for FBA. Expiration date is not currently an option, but minimum # of characters, minimum non-alphanumeric characters as well as a Regular Expression validator are options. You can
see the configurable properties here:
5) I don't know if there's a best - just experiment and use what best fits your environment. I believe many people use separate zones (mentioned in #2).