Procedure to apply for Copyright of Music Distribution

Hi, I'm an independent music composer and producer. I'm thinking of getting my music distributed through a distribution platform called CDBaby https://www.cdbaby.com/ I want help in understanding the different music laws that I need to be aware of and also I want to understand the various services they offer as I'm having a hard time understanding them due to my lack of familiarity with the laws. Also, I need to know that if I am the producer and composer of a song; where the tune is composed and arranged by me, am I entitled to be the sole copyright holder of the song? Considering that I have payed the singer or the instrumentalist for their time and effort on day of recording? I am asking this because there are a few songs I have composed which are sung by a different artist and I have credited them as singers and performers and paid them for their service. In such a scenario, what precautions should I take to avoid any possible disputes in the future?