Question about Installing Aprilaire Humidifer

I am planning to install an Aprilaire humidifier today, and I have a couple of questions:

1. What type of screws should I use for joining the ductwork and mounting the humidifer frame to the ductwork (size, length, etc)? I thought that I should use some type of self-tapping, but I was looking at the ones in my existing ductwork and they did not appear to be.

2. Should I use HVAC tape or silicone at the various joints, or does it not matter?

Thanks in advance for any assistance.