Windows – Skype for Business 2015 Edge server import certificate installation issue

Microsoft's best practices and design guidelines for Lync/SfB deployments suggest:

• Using a reverse proxy for publishing the external web services of Front-End servers.
• Placing the Edge servers in a position such that they are locked between two firewalls, one separating their public interfaces from the Internet, and one separating their internal interfaces from the LAN.

That said, it's actually quite common to use simpler configurations:

• The reverse proxy can indeed be replaced by a simple NAT, but you'll need to remap TCP ports, because the external web services need to be published on TCP port 443, but they are actually listening on Front-End servers on TCP port 4443 (port 443 is used for the internal web services).
• The Edge servers can have their internal interfaces directly connected to your LAN; however, please keep in mind that this is a potential security risk: if an Edge server gets compromised, it can (and will) be used as a bridgehead into your network; that's the main design reason for putting a firewall between it and your LAN.

It sounds like you're seeing two different issues. If the user you are using to access the Skype for Business Control Panel does not have the correct permissions, you will not be able to perform the desired actions. You want to ensure this user account belong to the following groups:

CSAdministrator
CSUserAdministrator
RTCUniversalServerAdmins
RTCUniversalUserAdmins
RTCUniversalReadOnlyAdmins

After you ensure proper permissions, log out and log back in. In the Skype for Business Control Panel, when you click Users, then Find, you are searching for Skype For Business-enabled users, of which you currently have none. You would have to click "Enable Users", then "add", then "Find". From here, you will see the AD users you created, and can then enable them.