For my money, April In the olympics? Maybe 50% half decent weather. Can also be perfectly clear for a week at that time of year or completely soaking wet for a couple days at a time. Generally fronts will move through fairly quickly that time of the year and hiking time is generally 50%. Bring Gaitors. Keeps splashed mud/water off your legs and out of your boots and socks.
I would look into the east side of the olympics trails. If you are bound and determined to go to the west side of the olympics, how about a beach romp? Take the beaches north out of Hoquiam. Also, I think its the Queets valley river trails that are far better though. Things to look into. Oh, yes, lots of hungry black bears that time of year as well...
As for Ranier, SNOW, SNOW, SNOW, SNOW, SNOW. You could wander around Longmire. You could wander around Ohpenocosh forest walk. Anything higher and you will need Snowshoes (small size generally at this time of year) as it will be melting and the snow will be slush making horrendous post holing without them. Crampons up higher? Doubtful this time of year unless you go WAY up where it actually freezes at night, then yes, of course. Ice axe, sure. If you are going to go up high... Good Luck, personally I would go for the Olympics up high instead of Ranier, as ranier will just be a giant snow blob without anything else around it. The Olympics on the other hand have mountains, ridges, DEEP valleys. Anything in the Olympics over 4k as well depending on the year we have had. Difference is that the Olympics have far more lower trails through Old Growth forest.
If you had the time, you could hike all the way around Ross Lake in the North Cascades. There is a section on the west north shore without trail though. If you don't want to do this take a boat ride back or just take the east bank trail back, or take a boat ride from end of ross lake to the Little Beaver Trail head and then hike back to your car bypassing the non trail portion of the west north bank. Ross Lake Resort is the water taxi service.
PS your clothes. Sound fine. Bring an extra under shirt/socks as they will get wet from sweat during spring temps and you will need something to change into when you stop at night, gets cold fast. Bag is more than fine espeically with your down coat added.
What kind of sleeping pad? It better not be a z thermarest as that time of year the temp will genearlly be "around" freezing if you are camping on snow and all those ridges will collect said condensation/persperation from your body as you will be camping on snow and condense said readily available water vapor into all those waiting cups in said z-rest and your B-Bag will get soaked. TO not have this problem change into dry clothes/use a Vapor Barrier system. Closed Cell foam on snow unless its really cold and then you can go back and use the z rest, but anytime its high humidity and near freezing camping, IE spring, DO NOT USE A z-rest. All it does is capture water and soak your sleeping bag.