Howdy Katy -
That's not a very long trip for 4 months. Only about 2500 miles?
Must you stay on ACA routes or are you willing to do your own?
Is Denver an absolute destination - or just an end point?
May I presume that you will be camping, primarily?
<<<>>>
I am guessing that you are not Westerners from your bear question.
Actually, nearly all of the routes you listed are bear country.
Only a small part in Idaho, Montana, and Wyoming is grizzly bear country.
The hanging method is no longer legal in most California national parks and forests.
Too many people did it wrong - and bears have figured it out.
Also, too many hikers/cyclists have terrible bear practices in the backcountry.
The banana or power bar gets forgotten in the handlebar pack.
And people use tents they have eaten or even cooked in.
The bear can smell food from two weeks ago, if you ate in your tent.
<<<>>>
I have done a half dozen loop tours of the West - usually all summer.
Here's one from 2005 -
https://www.cycleblaze.com/journals/wna2005/In general, the summer climate regimes of the West are like books on a bookshelf.
From west to east they change drastically - and present challenges for cyclists.
Pacific Coast - mild: damp
Coastal Ranges - warming; wet but drying out
Central Valley - hot; dry
Sierras & Cascades - cool to cold; summer showers
Great Basin - hot to very hot; extremely dry
Rockies - cool to cold; summer thunderstorms
Climate-wise, a summer loop works counter-clockwise.
California really is at its best in May - Yosemite's waterfalls are massive.
Early to mid June is a nice time in the Southwest - before the monsoons hit.
Late June thru July is a great time for the Rockies - following summer heading north.
I usually head into the Canadian Rockies, too.
From Glacier NP in Montana to Jasper NP is amazing.
Or you can head back towards the Pacific Northwest on the Northern Tier.
I would not head back into California in late summer.
Probably going to be a bad fire year from central Oregon south.
Extra time? The Olympic peninsula? Vancouver Island? Alaska?
(Although the rains really pick up in coastal Alaska after late August)
<<<>>>
I mean, if you are going to have 16+ weeks, 4000 miles is only 250 miles per week.
I was doing about 400 miles per week with major hikes - like across the Grand Canyon - pushing 50.
Given your backgrounds and what I can surmise, you should be able to do similar.
Yes, start moderately - but in the West the miles pile up easily - no latte shops to delay your start.
At a mere 330 miles per week - 5 1/2 riding days @ 60 miles per - that's 5280 miles.
You could hike Yosemite, hike Bryce Canyon, hike the Grand Canyon, hike Aspen -
hike Yellowstone, hike Glacier, hike Banff & Jasper, kayak with the whales off Vancouver Island -
And still have plenty of time for the cycling.
Best - J