Stand the pots on the heat mat, then you have bottom heat whether they are in a plastic bag or not. Temperature control can be tricky. You can also use heating cables in sand or soil beneath a group of pots.

High humidity can be helpful for some cuttings, but isn't necessary for Fuschias or Dahlias which are very easy. Rosemary I'm not sure. You can also spray the cuttings regularly and this is better than a plastic bag. Connstant 100% humidity can make cuttings rot, spraying is much safer and the preferred method for professionals.

You don't want to be heating the tops of cuttings because you will dehydrate them. No direct sun either. A north-facing window has enough light. Grow lights should be further away than you would for seedlings, you aren't trying to force them into growth.