20 domains on 1 server

[Oldserver]

Very basic questions, which I cannot find an answer to in the O'Reilly
Book.

I am setting up DNS for some 20 domains on one server, which is going ot
do everything: dns, mail and web.

1. I see others do this as follows (for each domain):

@     IN A     10.10.10.10
mail   IN A     10.10.10.10
www IN A     10.10.10.10

Now if my server is marc.venster.net, it could also be done thus (except
in the zone for venster.net of course):

@    IN CNAME marc.venster.net.
mail  IN A       marc.venster.net.
www IN CNAME marc.venster.net.

Why not? Extra lookups? It looks "cleaner", as otherwise this machine
would have a hundred hostnames...

2. All the zone files (or nearly all) will be identical. What do I do to
keep it "clean"? Copy the file 20 times to the different names or link
them with ln -s? Last option would be easiest in case a change is needed
some time. I understand the named.conf want them all listed. Or can I tell
it that e.g. db.basic is the zone file for all domains, like this:

zone "venster.net" in {
            type master;
            file "db.basic";
};

zone "venster.org" in {
            type master;
            file "db.basic";
};

zone "superputer.com" in {
            type "master";
            file "db.basic";
};

Thanks!

Marc Schneiders