By suspending do you mean site should not be accessible? I think you mean this as you said about stopping the service. To suspend the site by stopping the apache service, stop the apache service and stop the chkservd service, so that it will not restart apache.
From shell as root execute
service httpd stop
service chkservd stop
You can transfer the accounts from one server to another by using the "Transfer multiple accounts" option from the root WHM.
point dns / nameservers to park or trouble page you create.
if you have informed your users. Set up the reseller accounts on the new server. Keep the old server up, give the resellers the new ip. Most resellers have backups (or can get them from old server) and can be back up and running long before you can get the move done, and all the resellers individual accounts debugged because of slight differences between old and new server.
spend your time moving those that have no idea what they are doing and don't have backups.
Last week we waited 4 days for a host acquisition to move our reseller account to the new host server. Half the accounts never moved. After begging, they finally set up just our reseller account. We had all our accounts up in less than two hours from our backups.
As soon as we got the acquision email, we changed the affected domains zonefiles to run on a backup reseller account where we keep live backups of all accounts. Clients were down only a few minutes as the dns caching refreshed. Luckily, this was at 1AM. You don't move 24 resellers averaging 10 accounts in a few minutes, unless you unracked and moved your box, then you still have all the ip changes yet to do. I don't see how the resellers with a single server would survive what was a 4 day outage.
If you stop the chkservd, it will not get started automatically. Also apache service will not be restarted automatically with chkservd stopped. If you need more guarantee disable the apache binary temporarily using the following command and enable once you are done.