Hi Deirdre,
You can look at inquiry activities as both ‘science questions’ and as ‘design and make’ activities that use their own science understanding to inform the design process. As you have noted, it may take much longer than you have anticipated, so you may need to plan for practical maths as part of the activity to give you another aspect of the busy curriculum in the time.
I like how you included arts in stem – this is the current thinking about STEM & Arts.