I have the Opportunity of integrating an On-Premise Installation with SharePoint Online. There are about 100 employees using OnPrem, while only about 50 (External) would be using SP Online. The main thing they need is Federated Search, Sharing Documents, consolidating Emails etc.
What things should be considered before starting a Hybrid implementation? What would be some high level objectives I can put together?
You have to check what are your requirement, what kind of search hybrid solution you need. Currently SharePoint hybrid solutions: Search, Business Connectivity Services (BCS), and Duet Enterprise Online.
In search you have to decide which topolgy you need.
One-way outbound SharePoint Server 2013 Search services can query the SharePoint Online search index and return federated results to SharePoint Server 2013 Search.
One-way inbound SharePoint Online Search services can query the SharePoint Server 2013 search index and return federated results to SharePoint Online Search.
Two-way Both SharePoint Server 2013 and SharePoint Online Search services can query the search index in the other environment and return federated results.
You can learn more about it: Overview of hybrid SharePoint 2013 for technical decision makers
http://go.microsoft.com/fwlink/?LinkId=320740
You should also try SharePoint 2016 beta 2, MSFT announced a better hybrid solution in this version.
