simple network questions

[unixjingleman]

Hi there
I'm building a network with a topology illustrated below:

|internal system|---|switch|----|OpenBSD|------|switch|------|border router|

The OpenBSD box is a dedicated firewall that protects the internal network. Attached to the first switch(the switch that is attached to the border router) are my servers. So the servers are protected by the border router's firewall and their own firewalls, and access to the internal network, and between the servers and the internal network, is controlled by the OpenBSD box.
It took me a while to put dd-wrt on the border router so that this set-up is supported. The only questions i now have are:
1)would it be best to just bring up the OpenBSD's internal interface statically and to bring up the interfaces of machines on the internal subnet statically also. So that the OpenBSD box isn't doing dhcp for the internal network, it is just a firewall for it?
2)In which case should i have the border router as the DNS server for all the machines on the whole network?
3)Or would it be better for the machines on the internal network to get their I.Ps via dhcp, from the OpenBSD box(bearing in mind that the servers already get their I.Ps via dhcp from the border router) and have the OpenBSD as the DNS server for the internal network also?

Thank you for your time and any replies you might send
regards unixjingleman