Some people prefer 32 for reasons that are not clear to me, or even 28. Tandems can benefit from 48 spokes. Staying with 36 spokes offers the widest selection of hubs and rims. There are double-butted spokes that are narrower in the middle where there is less load, bladed spokes, wavy spokes, and other exotica. Bladed and wavy spokes are also more difficult to install because they twist and make it hard to gauge tension.
Spoke length is important, but computing the right length is a black art.
Generally, all spokes of the front wheel have the same length. When buying replacements bring an old spoke. Up to a millimeter too short doesn't hurt, but spokes that are too long can puncture the inner tube. 3-cross is standard. Obviously, each of these spoke patterns requires a different spoke length.