What's a good number for IOPS (RDS)?
A good number is rarely peaking to the available IOPS of the hardware or Cloud provider.

Your graph show rarely getting over 25.  That is a very low number.

AWS carves up machines and sells you different amounts of CPU and IO.  I can't say what your max is.

If you are hitting limits of CPU or IO with MySQL, then the first thing to do is to find the slowest query.  It may need a better index, probably a 'composite' index.  Or it may need to be reformulated in some simple way.  Only after that, I would look at tuning.  Then at hardware or AWS plan.