List of things that Redux doesn't do, or not completely, that I usually do for a customer:
Set up phones on all servers with an alphabetical suffix pertaining to the server position. So for extension 1000, the phone I create on server 1 is 1000a, the phone I create on server 2 is 1000b, the phone I create on server 3 is 1000c, etc. Then I create a phone alias of 1000x with phones 1000a,1000b,1000c in the list. This gives me load-balanced agent logins.
Generate a purely random password for the server's "Conf file secret" entry under Admin --> Servers. I either use the first 14 characters of an MD5 hash of the date + hostname + IP, or go to
www.strongpasswordgenerator.com and generate a 14-character string without symbols.
Modify /boot/grub/menu.lst, replacing the vga=something with nomodeset. This causes the system upon reboot to just use the standard BIOS framebuffer, as opposed to loading up VGA drivers, and switching to higher resolutions, and all that other garbage that is not needed and can actually slow a system down.
I will usually slave the NTP on the dialer and web servers with the Database server. This way you make sure everything is always in sync, irregardless of the state of internet connectivity. If you have multiple databases then you would slave to each of them. Just edit /etc/ntp.conf and change the server lines to just be your database servers, and delete the other server lines except 127.127.1.0. You can also just leave this alone, as by default all servers will attempt to connect to time servers on the internet.
I prefer to use IP-addresses in astguiclient.conf as opposed to domain names. We've had problems with some microsoft DNS servers being slow to respond, or when DNS goes offline.
Change the SSH port on the firewall so that it's something else instead of port 22. I then just make sure I add Port <XX> to /etc/ssh/sshd_config and restart. You should have two entries in sshd_config, Port 22, and then below it Port <XX> for your firewall's port forward. This way internally it's all the same, and externally it's different.
If you have a hosted model, a private LAN for inter-cluster communication, and an external WAN for offered services (Web and SIP/IAX). Yes, it's two NIC's per server and two networks/VLANs to manage. No, it's not a burden or overly cumbersome, just twice as many cables usually. And NEVER have the database on the internet. It's just bad.
Don't try to save money on the database server, save it on the web server and dialers. There is no way to short-change the DB and expect good results.
That's all I got off the top of my head.