A quick dig into the internet seems to support your supposition that the Celestial Court are the angels in heaven, collectively. Some articles (opinion pieces) support the Court with Saints included in the number, based apparently on the teachings of the Venerable St. Bede, a Doctor of the Church.
Catholic Culture made this article on the subject of angels. Also see this web site on St. Bede and summaries of his writings.
I have not yet found anything in official Catholic teaching, doctrine or dogma on the nature of the “Celestial Court.” Hopefully others may know more.