Do i really need to implement RDS Gateway if my RDS farm will only be used internally and not accessed outside the corporate network?

No, you can get away with just using web access. few less options, and the RDP connections go directly from client -> session host, but it works

Thins of RD Gateway as a Netscaler. It will allow the user to connect over SSL to the Gateway server which translates the connection to RDP to the Session Host. If the endpoints are all on the company network, you can just RDP to Session Hosts and the RDBroker will route them there.