Many parents ask how many activities they should have out. I had the same question when my boys were young. It's a balance because you don't want too many (difficult to look after and can overwhelm) or too few (don't offer enough choice). What is the magic number?
I put this question to the teacher in our parent-toddler class and her answer was around nine and not more than twelve. This number worked for us for all of the toddler years and I had a look around and it seems approximately nine activities works for other families too.
It would depend on the type of shelving you have and how many activities you have room for. If your child is at daycare or if you don't spend much time at home you might want less. If you have more than one child and the children share some of the activities, you might want more. For us, our nine or so activities included mostly fine motor activities with some matching or categorisation work. We always had additional materials around the home such as practical life materials in the kitchen and outdoors, books around the home and more. But this is the number for our puzzles and other activities set out Montessori style on trays.
Observation is key. All the materials need to be developmentally appropriate and attractive to the child. We try to have some activities that support the child and some that challenge them. If the child has lost interest in any of the activities then it is time to replace them. This is an example where you can get ideas from Montessori toddler communities but regarding the number of activities and how to rotate I have found the most relevant ideas and inspiration come from other families (examples pictured above).
I'd love to know how many activities you have out or if you are an educator how many activities you recommend to families.