Seattle to Butte Yellowstone Rapid City Medora.Best Route?

So we will leave end of May arrive early June.

Now the Route! Does anyone see any problems with this plan? Or have a better suggestion?

The route was I-5 to Seattle,
The I-90 to 359 to 287 south into West entrance of Yellowstone.
Back up the 89 to the I-90 to Billings.
Then 212 & 85 to Rapid City.
Back up the 85 to Medora
The I-94 to 83 & 5 finally 281 into Manitoba.