It is important that all tracks that are MONO are exported as MONO, and STREO as STEREO. Clear names of instruments and of course, stem number doesn't really matter.
It is not necessary! But usually customers send a complete song from which i make a short time, or exact requested time of the part of the song.
As for mixing project, the best way of sharing is directly over WeTransfer. After contacting us first, you will get a code that you will write when you send files.