If you are making an MP3 compilation, yes. If you are making an audio CD, no.

For MP3 CDs, an MP3 encoded at 128kbps will have a smaller file size than one encoded at 256kbps so you will get twice as many tracks on a CD-R.

For audio CDs, the MP3s are converted to CDDA so the relevent factor here is time. A four minute MP3 encoded at 128kbps is exactly the same length as one encoded at 256kbps so file size / bitrate doesn't matter. Most CDs hold around 70 minutes of music so you'll get approximately 17 or 18 audio tracks on a CD-R.