Been out that way a few times. There is a lot on the way there but you probably want to spend most of your time in the Black Hills and to the west.
You are very smart in planning early for the trip, especially Yellowstone. The above info gives good ideas. California might be a stretch depending on your riding style since you are looking at 1500 miles to the Black Hills and there is so much to see with Yellowstone and Glacier. However, just last summer at age 66, I made a motorcycle trip of 9,000 miles in 18 days (15 riding) and still saw a lot and still enjoyed a lot.
You might consider looping back home by way of SE Utah. It may be hot but if you prepare and dress properly with plenty of water it would be worth it.
July might be a better time for weather in Yellowstone & Glacier but more tourist families. One time while in a car during mid July we arrived in Yellowstone the day after one of the passes in the park had just reopened because of snow. In late July 2009 I rode through some very light flakes of snow in the same area.
If you want to stay in Yellowstone either camping or lodging you need to make reservations. The last time I had a very nice place in Canyon Village near the Grand Canyon of the Yellowstone but made reservations 9 months out. Once in a travel trailer we made reservations several months out. Even back in the mid 70s we had to pitch our tent the first night in overflow tent area.
212, Beartooth, is awesome. I went one way years ago by car then just a few years ago I left Yellowstone and ran it east. It is one of my all time favorite rides.
You might consider Devils Tower National Monument. Also, I have always found the Little Bighorn Battlefield National Monument interesting. So many fictional movies have been made of Custer and the battle it is good to find out the facts. Now they show not only where the soldiers fell but also where the Indians fell.
Going to the Sun Road in Glacier is another one of my favorite rides. In 1974 I traveled west to east in a car then just last August I rode east to west on my VTX then circled around on US 2 back to East Glacier. Even with the fires it was still a great ride. The tour buses slow you down some but they are always pulling off somewhere after a while but I just enjoyed the slow pace at a distance behind them.
May I recommend a Motel in East Glacier? Pine Mountain Motel, it is old, small, very clean, low priced, owner is very nice, and a very relaxing "court yard" for a lack of what to call their lawn with picnic tables. Food and drink are within walking distance. East Glacier is cheaper and less crowded than West Glacier.
You have so many choices. I love those kind of challenges. If you make it farther west a complete new set of choices open up. Yosemite's Tioga Pass Road is great. Sequoia National/Kings Canyon National Parks (Red Woods) are great too.
You make me want to go again but I have to concentrate on my bucket list this summer.
Enjoy yourself and be safe.
My VTX as used on Race Tech site.I'm67
rode to 49
States+DC & 11
on my '07 Black Cherry VTX1300R
w/aux tank, Race Tech Gold F&R
,Mean City Cycle, Motolights, Glen's Light Bar w Rivco H-4 aux headlights w/SS Utra bulbs,Radiantz LEDs,Baron tach,Marlin therm&clock, PowerLet,Break-A-Way,K&N, IBA: 2xSS2000,12xSS1000,4xBB1500,2TX1000,NPT 29/76; Lake Superior Circle Tour