Thanks I really appreciate what you said, I'm gonna check what I can do, but there's something I was wondering, how can I find the key signature of a song and change is key. I know what the key signature are, but beside that, I know nothing and it looks like all the mix I have done so far have this big problem.
For the second point, yea, I always got this kind of problem, like I said in a early post, I'm always switching instrument, can past more than 1 hours only searching for instruments that can fit, and finally get something, decent or just ok... but I think this problem will get solve with time and practice, I will revisit this song for fun, looking at what I can do.
And finaly, the 3rd point, well, that was the part that I try to put some kind of background melody and fail miserably.
I know I'm getting better and it's a relief.