Congratulations on your rating, Tami!
I also have MS which I anticipate a rating for within the next few months. When I filed my claim, I included a lot of my residuals and secondary conditions. It has been a 2-1/2 year battle getting the MS service connected, but I'm quite confident now since the RO has finally scheduled C&Ps for the residuals and secondaries. My MS is secondary progressive and I am totally disabled.
I am certainly no expert on VA claims, but I would suggest that you file for all of your residual conditions as well as filing for IU. It may be possible that your residuals will get you to the 100% mark which would make IU a moot point, but if not, you will already have your IU claim in. Remember that things like depression, cognitive dysfunction, muscle weakness, spasticity and overwhelming fatigue are a few of the very common issues with MS.
I wish you the best in getting an increased rating.