Network setup

We are small hosting company and growing fast. The current network setup is
almost 3 years old and it was built before. Not that it was designed bad but
it can't scale to the growth we are experiencing. In the next couple of
months we will be making transition to a new network and the design of
server infrastructure falls on my shoulder. And since I have only a year of
experience doing this I will need some help. Following is the current
scenario:

- We are using a hosting center and we are puchasing two network blocks
(VLANS) each with 12 ips.
- We have 4 webservers and a mail server. We will soon be adding two more
webservers and add redundancy to our mail server. Thus three more servers
are coming up.
- Currently a home-brewn iptables-based firewall does the NAT for the
netwrork.
- This firewall also runs an internal DNS for the webserver and the
mailserver, which was decision made due to lack of resources. This will
change.
- On the same network, we have a backup server which backs up all the
machines every hour and mail server every 15 minutes. We have three levels
of backup spread over three different places independent of this one.
- Right now data traffic is less than 100GB/month. But, if that jumps up
considerably by next year Q1, I wouldn't be surprised.

Now this is what I am thinking about:

- Split the responsibilties of firewall, routing and internal DNS across
various machines or appliances.
- I want to provide redundancy for these three. I have had nightmares when
the firewall just died on me.
- Put a remote KVM switch to control all the servers. Not very important,
but sometimes it can be helpful.

Now what is the best way to set it up such that I can take most advantage
out of our network up at the hosting center? There is very good possibility
that we might getting another (or two more) networks if we keep growing at
the current pace. Ideally, the new setup should easily be able to accomodate
that. Our hosting center also provides a very good SAN infrastructure for
decent rates. I might be even willing to consider a cluster environment if I
am convinced that it is the route to take.

Any suggestions on what kind of appliances/software/hardware to buy to
accomplish a higly available and scalable netwrok? Please do bear in mind
that so far I have only set up small networks as described above. Thanks.

--Turi