New cert required for deploy office 365 hybrid on existing exchange 2010?

Dear all

We want to deploy the existing exchange 2010 (CAS/Hub + MBX) to the office 365 hybrid deployment.

I will setup a ADPF server and Active directory sync server. All servers will setup in internal network.

So, as we already have a SSL cert on CAS server, do I need to create another cert for office365?

On the other hand, seems I need to prepare a public IP for the CAS/Hub server to communicate with Office 365. Do this IP need to publish at external DNS?

Thanks