Is there a particular reason you need to use Earth? For route planning I find GMaps enough. Earth just gives more of a 3d look, which may help in visualizing some mountainous routes. But GMaps has both a Sat view, and Terrain mode (current found in a left menu, or the layers icon on Android). And for this route there aren't any mountains to worry about. The Black Hills are the first ones you come to (after leaving the NY Catskills).
GMaps gives several alternatives, highlighting the one that is fastest. Equally important it shows the distance. If alternatives rank differently in distance and time that means the estimated speeds are different.
Boston to Rapid City is about 1900 miles, and 28 hrs. GM also shows some construction and slow downs.
Do you know that you can tweak the routes to explore alternatives? For example if I grab a route near Chicago and drag it down to Indianapolis, miles increases by 40, and time by 1 hr. It is still all freeway, using 71, 70 and 74.
An alternative that stays on 80 past Chicago, turning north at Iowa City has about the same time and distance as the originals.
Some suggest taking I39 north to Wisconsin (as sort of a outer beltway for Chicago). But that is a bit further than the Iowa route, and hits the construction and rough road others mention for I90 in Wi and Minn.
So on a long run like this, alternatives don't change the travel time by much - a hour or so either way, 60 miles plus or minus. How long you stop for meals and lodging will affect the travel time more than the route.
As for safety - maps aren't going to tell you anything about that.
Another trick with GM, is to specify a departure time. It's probably best for shorter segments. For example if you want to explore travel times through/around Chicago at various times of the day, pick a route from Elkhart IN to Madison WI. It may also show you where to expect most congestion.
As for bypassing Chicago:
I80 still goes though the industrialized south side and NW Indiana; it has typical rushhour traffic, as well as being a funnel for EW truck traffic. But it often moves, sometimes too fast for comfort.
There isn't a good alternative. US30 is the next highway to the south, but it's stop and go urban city street for a long ways. There are more rural state roads further south, and US24. But it's hard to tell which ones a reasonably through roads. But you can pick a route, zoom in, and get as close as a Streetview to see how many cornfields you'll be passing.
