Customization - Work Around Needed

We are an enterprise customer and are really struggling with not having the following abilities:

1. We need all users to be able see an account listing without seeing full details.
2. We need any new leads to be cross checked in our entire system for duplicates prior to turning into an opportunity so that we can prevent multiple people from working the same lead.
3. We really need some shared calendars with permissions.

I have written in the forum before, but no one ever responds. Can someone PLEASE reach out and help me with this. How do other companies segment their information?