This is a great start! I don't wanna pull ya down! You're on the right track.
Things to work on:
You've got really great ideas going on, just need to keep on practicing and practicing. All this made from scratch is really awesome man. Took me a long time before I made my own synths, etc.
Keep at it!
I have to concur with what you have said. Mixing and Mastering are not my strong points, especially when working with LMMS.