Branch office setup questions

Hi all,

First of all thx for all the support from the whole community.
Since a few months now i’m playing with asterisk and the topics on this site helped me much.

I’ve installed on 3 CentOS5 boxes Asterisk 1.4.21 + GUI 2.0 on all boxes i’ve setup some sip users configured some analogue outbreaks and even managed to connect them to each other via a IAX2 Trunk. so i’m able to call User extensions on the other boxes as i’ve set the dialplan to dial 1XX, 2XX or 3XX over the corresponding trunks. there will be another 24 servers once i’ve setup this part to my likings.
Most has been configured with the GUI of course little interaction of the CLI.

But at this point i’m a little bit stuck and hope someone can help me out or putting me into the right direction.
What i would like to achieve is that we can use the directory, forwarding, parking calls, etc throughout the whole structure; so when people dial the directory on the 1XX pbx the can enter the last name of someone of the 3XX pbx.
An other thing i would like to achieve is all of the servers have a local PSTN or BRI outbreak we would like to use those outbreaks to dial from the remote locations through those outbreaks if it meets a special dialplan so long distance will still be billed to us as local.

i hope we can keep the GUI as it will be very complex for other support staff to configure everything through the CLI, dont mind to have an config through via CLI but at the end most of it needs to be maintained via the GUI, i think this will make it more complex but some sort of GUI is needed.
these are the main difficulties at the moment, i hope someone can help me out with the config of these options or at least point me into the right direction.

Thanks in advance,