a. You will not need to pay anything (it is royalty free right?)
b. You will not go into trouble by signing lots of papers
c. You will definitely need a music library where you can find lots of related music.

Let me help you on this. When you search Google for “royalty free music”, the result is endless you basically does not experience trouble looking for the right music for your project.

Before proceeding further, let me give what you need to license pure “royalty free music”:

1.) Most websites asked you to pay for a single (one time) fee to use their entire music catalog. That is fair, but you should double check with them if you are also required to pay “performance royalties” for the songwriters and publishers involved.

If they say no, make sure this term is stated in the licensing agreement that you are not going to pay even a single penny to performance right societies.

If this is the case, all of their songwriters and publishers are not affiliated with ASCAP, BMI, SESAC or any other performance right organizations.

2.) Another things you need to check carefully if the synchronization license fee is free. It is because it might be possible that you pay to use the songs in their music library but may end up paying again if the songs are successfully included in your film projects.

3.) You should also be careful about licensing mechanical rights. For example, if you license with them under the condition of royalty free music license. Make sure the mechanical licensing fee is also covered.

Maybe what they are claiming to be royalty free is just the performance licenses but not the mechanical rights. So if this is the case, you will end up paying for the use of their music when you include it in the CD sound track compilation album.

4.) If they are claiming it to be royalty free, it is also important to ask them what differentiates their material from “public domain music recordings”.