This article is from the CD-Recordable FAQ, by Andy McFadden (email@example.com) with numerous contributions by others.
You can have up to 99 tracks. Because the track number is stored as a
two-digit decimal number starting with "01" (BCD encoded, in case you were
wondering), it's not possible to exceed this.
Tracks must be at least 4 seconds long, according to the standard.
In practice, CD recorders have different notions of how short a track can
be, but most recorders will refuse to write a track shorter than one second.
The maximum number of files depends on the filesystem you're using. For
ISO-9660, you can (in theory) have as many as you want. In practice,
DOS or Windows will treat the disc internally as a FAT16 filesystem, so
you are limited to about 65,000 files if you want broad compatibility.