what would be the best way to have all of parts heard for a busy orchestra song that has many parts playing at once

If i have a song with many instruments playing at the same time for some parts of the song, what instruments would be best to use so that all of the parts are heard? For example, should I have a separate instruments for both a violin and cello part that only uses "arco" , would it be better to combine the two instruments instead by using the "strings' instrument and then assigning the arco channel to "violin" and the "tremelo channel to "cello" for instance to be able to hear all of the instrument parts played... or if I have both a bassoon and oboe part, would it be better to combine those two parts as "winds" and then assign each voice to one of the two wind channels (voice 1 being oboe and voice 2 as bassoon)... or both the the guitar rhythm parts (electric guitar and bass), is it better to combine both those parts into one part (having the "accoustic bass guitar" instrument with many channels to assign each of the separate guitar instruments or keep the guitar instruments separated as " berda, bass guitar, electric guitar, and ukulele instead) so that all of the instrument parts are heard more easily in a busy piece?
Basically in a nutshell, is it better to have separate instruments or have combined instruments parts to hear all the parts played in a busy song with many orchestra parts playing at once and not have some parts covered up or lost when the song is played back?