The role of reverse zone files

I'm in the process of setting up an educational (for me!)
network using SBC/Yahoo's DSL service with 5 static IP
numbers.

The domains registered are zefox.com, zefox.net and zefox.org,
with a prospect of reverse delegation from SBC/Yahoo once I get
two nameservers running. Unfortunately they're on the same subnet
(mine), but if they fail it'll disturb a very small population 8-)

Forward zone files for each domain make obvious sense, but
I'm a little hazy on the role of reverse domain files: Any nameserver
with forward zone files can tease out reverse information; what's
the need for reverse zone files?

There are only 5 addresses in the reverse file for all three domains;
will one 5.161.64.in-arpa file suffice or are three (one for each domain)
required on both nameservers? How would they be distinguished?

The DSL modem/router is configured to run a private class C network
on the LAN side and map selected private addresses to the public
WAN side. In principle that accomodates addresses for 253 hosts with
five hosts being accessible to the outside world. Is there a trap?

Far as I can tell this arrangement isn't discussed in the manual
I'm using (Hunt's "TCP/IP Administration", 3rd edition). Somewhat
to my surprise the Berkeley campus bookstore didn't have a copy
of "DNS and BIND" in the O'Reilly pantheon. Times must be changing.

It looks easiest to cope with the "dual horizon" problem by using
/etc/hosts files on the internal side; am I mistaken?

Thanks for reading, pointers to FAQ's would be appreciated.

bob prohaska