for july/august i'd ditch the medium weight top and bottom. not familiar with the paramount pants, but if they have decent wind/water resistance i'd also ditch the hardshell pants. i would ditch the light fleece and replace it with something equivalent to a patagonia hooded micropuff. you will be happy to have a warm hooded jacket if the weather goes to s#!t. with a micropuff and a highly water resistant hooded windshirt, i'd ditch the hardshell jacket, but that's me. i'd switch out the apex gloves for a warmer pair or bring shells to go over them. gaiters are a must. If the weather is truly bad at muir you stand a good chance of getting spindrift in your tent, but it will be more of an annoyance than a big problem. figuring out your sleeping pad is important because you will be on snow unless you opt for the public shelter. don't forget to bring good sunglasses with side protection. goggles for just going to muir might be overkill. hiking poles will make your life going up and especially down much easier. and don't forget, a lot of gear decisions can be made in the parking lot at paradise when you get an idea of what the weather will be for the next day or two, with the understanding that a forcast for rainier is always suspect. don't forget to bring extra food and snacks for an extra day at muir if things happen to go south.
you want to go here: http://www.nps.gov/mora/planyourvisit/upload/camp-muir-route-with-get-your-bearings-map-oct11.pdf and print it to have in your pocket and use as needed.
this is also another good web site for weather: http://www.atmos.washington.edu/data/rainier_report.html
and here: http://mountrainierclimbing.blogspot.com/
have fun and be safe.