Let me tell you about a way of making money out of doing it just on YouTube.
If you're writing music, the best way to do this is to pick one channel and make sure you're the king of that channel.
Don't try and spread yourself across all of them because you won't be able to promote yourself within them. The way that you promote yourself on YouTube with your music is you'll put tracks up that are within your genre.
You then link your tags, descriptions, and everything around that as a genre and around other artists that are similar to you. That way the algorithm will pull you into to their feeds and their sidebar. Also from that, you want to be able to write tunes that vloggers can use. With the descriptions, you also want to have a link where it can direct people to your main website or where they can buy the track from.
Now, you need to mix it up a bit for a lot of the tracks. So some tracks you'll be paid for, some tracks will be free for people to use. For the ones that are free to use, make sure you make a big song and dance of that and send those off to as many vloggers as you can find on YouTube. Tell them that they can use your stuff for free and all you want is a link in their description or at the end of their video linking back to your channel. What you're trying to do here is you're trying to build your channel's subscriber base, which will then be fed in from all the other channels.
The goal is to build YouTube as your front end and make money on the backend. The front end is that you're going to give a load of tracks out for free to draw people into your music so that they can find the links. Then they come to the back end, and they buy your stuff, and then you get some fans which build you as an artist and as a sound, as a genre.
Doing that across every single channel will take a massive amount of time. That's why I say, pick one platform, own that platform and then mail as many peopleon there. Direct message them and let them use your tunes for free so that you can link back to your content and you can upload more and more content, and then you'll get recognised, and you'll make some cash.