I need to modify 600 zones, 4 servers other resources with new class C info - advice needed

[pancho]

We are changing the way our network connects to the internet, and I need to 
change a LOT of IPs. (they don't want to buy the class C's)
Our name servers, web servers and early websites are hosted at those 
addresses. I understand that I need to get the boxes operating on the new 
and old IPs at the same time, and make our present DNS servers #3 and 4 at 
and register the new IPs for the name server as NS #1 & #2.
I'm looking for advice in two forms - a plan of attack and how, (in a Unix 
operating environment) do I change a lot of zone files?
1) Some concerns- it it possible to redirect request for resources that 
were on an old IP to a new IP via DNS? (I know how to do this in 
httpd.conf, I think)
2) How do I change 600+ TTL  fields in the zone records to an hour without 
all at once? (please don't laugh, I am new to this). I just finished 
reviewing and corecting all the files just using "vi". Also, do I need to 
change any other field?
3) is there something I can set up in the reverse DNS so that requests for 
resources at the old IP will be redirected to the new one?
4) Is there something I can do for our domains that are name-based hosts so 
that the transition will be smoother?
What else do you think I should be aware of?