Can i install symantec agent only first and later on install other features.
 

You can although it offers you no protection. You can always add ones later if you wish.

Follow this article if you wish to add other components later on:

How to add or remove features to existing Symantec Endpoint Protection (SEP) client installations

Yes you install the feature according to your required. Create the custom package.

How do I create and configure a custom Symantec Endpoint Protection installation package in version 12.1?

https://www-secure.symantec.com/connect/articles/how-do-i-create-and-configure-custom-symantec-endpoint-protection-installation-package-vers

Creating a Custom Package in Symantec Endpoint Protection (SEP) Small Business Edition (SBE) 12.1

You can modifed it when you require

How to change the Installed Feature Set on Symantec Endpoint Protection 12.1 Clients