Breaking up a large zone

[Albert Meyer]

I inherited a DNS server which serves a /19 plus assorted /24's, /22's etc.
The main zone (waller.net) has several thousand hosts, including about 2000
dynamically assigned IP's. The previous DNS administrator used a somewhat
bizarre rDNS-like naming scheme, for example, the name associated with
208.24.44.55 is 55.44.24.208.dhcp.waller.net. Apparently he did that to
break the domain into class-C-sized chunks which would be more manageable.

I'd like to do something more sensible, such as
208-24-44-55.dhcp.waller.net. The problem with that is that db.waller.net
would have thousands of entries in it. Would this be a problem? I have a
couple of ideas to fix it but I'm not sure what would be the correct thing.

One idea is to break it into subdomains, like this:

zone "waller.net" {
type master;
file "db.waller.net";
};

zone "dhcp.waller.net" {
type master;
file "subdb.dhcp.waller.net";
};

zone "t1.waller.net" {
type master;
file "subdb.t1.waller.net";

Is that the right way to do it, or should I have one large zone file, or
would it be better to use $INCLUDE to break up the zone into smaller files?
I read about creating subdomains in the cricket book, but it looks like the
method they discuss would result in a single large zone, and I'm not sure
that having thousands of hosts in the zone won't slow down my server or
cause other problems (the example has three hosts).