You will get spotting with the Mirena. For me that lasted around 4 months (not recently, I used it for BC back in the day). There is absolutely no need to finish the course of this Femeston. If you are worried about bleeding before the fitting, just keep taking the tablets until the day before fitting and then get it fitted. Start your patch as soon as you get them. It will take a while. But my experience of the Mirena was great after the first 4 months. Pretty dismal at first though, so don't give up. I felt tired, fat, bloated and got bored with spotting all the time. And then - bam! - no periods and I felt fine. I had it fitted because my periods were getting heavy and painful. It cured it all.
I wish I had understood more about menopause then though. Specifically peri. Because it was the best BC I ever had owing to the fact that it killed my sex drive dead! Stone cold. I now realise that I needed some oestrogen and possibly testosterone at that point, that was why my periods were getting so heavy and painful, my hormones were going out of whack. Full treatment then might have prevented a pretty dismal time in the past 6 years.
Good luck. It will be much better.