set up exchange 2010 server after migration to office 365 as a relay server

Hi,

We currently have the following setup
•      Exchange 2010 SP3 server setup in a hybrid deployment with Office 365. All mailboxes have moved to office 365.
•      Dirsync is used to sync up the AD accounts.
•      On the Hybrid deployment wizard emails are set to use the exchange server to send external emails and not office 365

I have read the following document

http://blogs.technet.com/b/exchange/archive/2012/12/05/decommissioning-your-exchange-2010-servers-in-a-hybrid-deployment.aspx


I understand that we need to keep the exchange tools so we can create remote mailboxes so it creates the necessary fields in AD.
What I would like to do is setup the exchange as a relay only server so our internal applications and devices can send emails to our internal exchange server and it gets relayed to office 365.

So am I correct in thinking I need to carry out the following:

•      Run the deployment wizard again and set the external mails to be sent from office 365 instead. Update the MX records to point to office 365.
•      Remove the database role from the exchange server – is there a guide just to remove this role only
•      Leave the hybrid deployment so emails can be relayed to office 365 and if the exchange goes down emails will still working fine as its going through office 365 (except the relaying emails)

For the hybrid deployment to remain would I still need to renew the SAN certificate for the exchange server when it expires so the exchange can still relay the emails?