Questions about placing a firewall between the current Adtran router and the LAN.

We have an Adtran NetVanta 3200 that is currently configured with a public
address 1.2.3.4 (WAN) and a private address 192.168.1.1 (Ethernet). It does
not handle all the firewall functionality that we need, so we bought a
SonicWall TZ170 to place in between the Adtran and the LAN. The Adtran 3200
splits the T-1 for both data and phone, so I cannot just do away with it.



It is my intention to change Adtran Ethernet port to 10.0.1.1 and then
configure the SonicWall with the WAN port at 10.0.1.2 and the LAN port now
at 192.168.1.1 so we don't have to change any internal configuration. This
leads me to a bunch of questions that I hope someone can answer:



1) Should I get the ISP to assign us a set of routable addresses for
the link between the Adtran Ethernet port and the SonicWall WAN port or just
use the 10.0.1.x addresses as intended? Are there any downsides to using the
10.0.1.x addresses?

2) Are there any issues with the router routing over the 10.0.1.x
segment, normally a non-routable segment. I think these SOHO-type units are
usually configured by default to ignore that RFC on an Ethernet segment,
aren't they? What is the name of this setting if I need to look at it to
change it?

3) Can I set one of them up in transparent mode, making them a bridge
instead? If so, which one, the Adtran or the SonicWall, and what IP
addresses do I assign and where? Would I keep the Adtran with the
192.168.1.1 address that it already has, then set the SonicWall WAN port to
192.168.1.2 and the LAN port to 192.168.1.3 in transparent mode? I am very
confused as to how this works. Is this even a good idea?



I have done only some routing but I normally have done just pure data T-1's
and the ones that did split the signal for voice and data already had a
routable address there too so I am just not sure about this configuration.



Thanks a lot for your help.