1. Starting with original works teaches you how to write better music without using someone else's artwork. Remixing is like redrawing a painting with differences, it doesn't really teach you how to make your own painting from scratch.
2. Programming from an initial patch is a very great skill, but a lot of people just find a preset they like and tune it (tweak the parameters) to their liking. That's perfectly fine; presets are there to be used, either exactly as created or as a template for a new sound.
3. Everyone's different. A lot of artists who make rock or similar genre music in DAW's like Cubase write out basic parts for their songs and then fill it in with more instruments and produce it better later on. People like me tend to make the song in a pure linear fashion, once you make the beginning, it's done and polished, and you move on the next part, produce/polish it, move on to next part, etc. I can say as someone who started out with the latter it's pretty hard for me to just write a track unless I'm really getting good inspiration (because I won't know what the next part is when I'm done the current one). Outlining your track can make it easier to stay with it and not get bored of it.