I am in the process of building a custom 5 string fretless bass. Since I am new to this what electronics and pickups is a good choice? I've only checked out bartolini pickups right now. Also, if it helps at all I am using mahagoney wood for the body, bubinga for the neck, and possibly indian or brazillian rosewood.
Ask yourself what kind of bass tone you like. If you like the sound of a Jazz bass, get Jazz bass pickups, for example. That would be the most common choice for a fretless bass. Or maybe a Precision is your thing, or a Music Man Stingray, or double-humbucker, etc. It really is endless. Think about tones from music you like, then research the type of bass used.
Aero Jazz bass or music man would be perfect for your custom bass if you like its sound acoustically. Best of luck!