OK, thanks for entering (hope you can help)
The 2 servers are cpanel boxes, on the same network & router.
Reason for moving: upgrade + better partitioning on new server, so swapping HDDs is not a solution.
Box 1 (existing server) has its 20 IPs used by server's ns, sites and reseller's accounts.
Box 2 (new server) has 5 IPs.
I have no problems moving the accounts (files, DBs .. etc), it is the technical steps to avoid down time that I am not sure of.
1- Box 2 will have exactly same settings as Box 1 including main IP & name servers, same IPs assigned to reseller accounts and sites
2- Minimun downtime if any.
3- Box 1 will be reset when everything is ok on Box 2.
Please treat me as a newbie (I am still one)
Thanks for trying to help