There are couple questions here, I will try to address one by one
You will probably want to push inputs.conf to monitor a file and not props.conf,
this is a great wiki page that explains where conf files go: https://wiki.splunk.com/Where_do_I_configure_my_Splunk_settings%3F
to automate this process across forwarder (and other splunk instances) you can use one of your splunk instances as a Deployment Server. According to your architecture description, your Search Head is the best candidate.
here is docs on how to configure deployment server and deployment clients (pay attention that Indexers can be clients too!): http://docs.splunk.com/Documentation/Splunk/6.6.0/Updating/Configuredeploymentclients
now you can build small apps that will carry configurations such as inputs, outputs, props and more!
create serverclasses and assign clients and apps to groups, now you can control your Indexers configuration and forwarders configurations from one single machine.