Which version of EBS ? The 12.1.1 install does not support a RAC install - you will have to perform a standard install and then convert the database to RAC.
R12.2 supports a RAC install - http://docs.oracle.com/cd/E26401_01/doc.122/e22950/T422699g54568.htm#3801603
What is the work flow ?
For 12.1.x, do the installation on single instance then migrate to RAC.
Oracle E-Business Suite Release 12 High Availability Documentation Roadmap (Doc ID 1072636.1)
Configuring and Managing E-Business Application Tier for RAC (Doc ID 1311528.1)
For 12.2.x, Rapid Install supports RAC -- http://docs.oracle.com/cd/V39571_01/current/acrobat/122oaig.pdf
Can I start setting up Oracle RAC with two nodes and then install EBS on the third node.
While installing EBS can I specify it to use the cluster I creaed earlier ?