If I am using an MSM and collecting data on a monthly basis, am I restricted by the amount of data I can collect and upload?

The amount of readings you can take per month depend on which tier of licences you are currently using.

Licence tiers range from 1000 readings a month to 250000 readings a month.

 

If you are on the legacy style of licences based on the hardware you have then no you are not limited on the number of readings you can upload each month.