Looking at the Indiana Traffic Count Database, I personally would not use US-52 as it has high traffic counts 5k+ to at least Morristown then it drops to only a low of 3k before Rushville. And these are 2020 counts when the traffic was presumably lower due to covid restrictions. Both with little to know shoulder.
After Rushville, it gets better at around 2k but then starts to pick back up before Brookville. It gets worse the closer you get to Cincinnati.
Honestly, I would just use ACA's maps from Indianapolis to Xenia and then back SSW to Cincinnati. If you want to shave a day or two, you can try to create a route using county roads using Indiana & Ohio's traffic count maps and county road maps. You can also check out Strava's heatmap
https://www.strava.com/heatmap#12.28/-96.00936/36.15376/hot/ride to see what roads local cyclists use. Remember though that you can have 1 cyclist who rides a particular route every day to and from work thus potentially making it a "popular" route (thus presumably somewhat safe), However, in reality it may be the rider is just much more tolerant of heavy traffic, big hills, etc. on the commute and the route is not good for loaded touring.
My guess is the created route will take 3-4 days using county roads assuming around 50 miles per day. After you spend a few days creating a route that has low traffic, services, etc., you will see why ACA maps are so nice.
If you want to go to Louisville instead, I have a route I can send you. Sorry I could not help you further.
Tailwinds, John
