Extend AD schema for office 365

Hi folks,

I know what needs to be done to get exchange ( office 365 in our case) attributes in on prem AD.  never had onprem exchange server.

This is require as we have SSO enabled by AAD connect . 

AAD connect is setup and configured on other server standalone not in DC/AD Server.

queries:

1) Now the question is should I download Exchange in our actual AD server and update schema  and then refresh/select those attributes in AAD connect app.

 2) Before performing this change in AD schema. Is there anything, I should put into consideration except AD backup by system state?

last but not least - is there any other way we can have  exchange attributes in on prem AD for SSO by office 365 Azure AD.

Thanks

Atul