SQL developer licensing SQL developer is free or do you require license for oracle database to use the sql or pl/sql developer? Also, Is it secure to connect to the oracle database since it connects to the db over a remote port right?
SQL Developer the client application is free of charge.  Of course, the Oracle database would need to be licensed in a way that allowed you to connect with any tool.

PL/SQL Developer is a completely different tool produced by a different company that you would need to license.

Define "secure".  Assuming a default database install, using any tool to connect to the database is secure in the sense that, say, the password isn't sent in clear text over the network.  But all the data is, by default, sent in clear text unless you configure Advanced Security.  But there are many, many ways that a database could be relatively secure or relatively insecure because there are many, many ways to set up security and many types of things that people may want to prevent.