No, that's ok. If you run without -d, Ajenti continues to work, attached to the console. -d runs it the same way, except it detaches from the console. The right way is to run service ajenti start (which will run service with -d and track it).
The error message you see comes from the update server, it doesn't affect functionality of your panel.

SSL23_GET_CLIENT_HELLO:http error usually means HTTP:// and HTTPS:// are messed up in the URL.

Yes, you can edit the /etc/ajenti/config.json file and replace the port value.

Here are two quick diagnostic steps you can take:
1) check Ajenti startup: run service ajenti stop; ajenti-panel -v. You'll get some output if Ajenti starts normally. While it runs, you can go on and try open the panel page in the browser.
2) check network connectivity: run apt-get install netcat; nc -l 8000. Then try to open http://<ip>:8000. If the connectivity is ok, you'll see browser request in the nc output.

Can you verify that no firewall or NAT is blocking the port 8000?

This would be a problem if your Apache configuration already uses port 8000 for itself.

Yes, it's definitely possible. Have you seen any error messages during installation? If you don't remember, it's safe to run install again.

I changed the default <label>. I would recommend simply making a custom style for label (CSS rule .control.label.style-stylename).

What do you mean with "normal word flow"? Default value for CSS white-space is "normal". However I have committed a change from w-s: pre to w-s: pre-wrap, which will let you wrap text when a <label> is constrained within a size-limited <box>. 

Plugin available in master, with ntpd integration