John & Lisa, Welcome to the ACA Forums!
It sounds like a wonderful trip you have planned. A couple of thoughts. First, you don't say how many miles a day you plan to average overall, if you have a deadline , i.e. must end by August 1st, and/or what towns your family and friends live in. That can change what I am about to say as my answers are based on the "typical" 55-60 miles per day overall (including rest days).
Early May is a bit early as several passes may still closed due to snow. Additionally, it will still be somewhat cool. For instance, in late May, Missoula's average high is only 70* with a 5* range common. The average low is 45*. There is a somewhat high chance that Going to the Sun highway in Glacier National Park will still be closed and late May/early June is the season's highest chance of rain at 35%. It sucks to ride it in the rain as not only do you miss a lot of scenery due to clouds but the descent is miserable due to the wind chill. I speak from experience. The rest of the trip the temps would be nice. Check out WeatherSpark.com for a huge database of climate data. If you can handle the cool weather and possible detours due to closed passes, this time is fine. If you can start later, I would suggest that.
As far as the route goes, I can't tell if you mean you will take the Lake Erie Connector all the way to Buffalo and wing it down to Philly. or down to Sandusky and eventually connect to the Chicago to NYC route into PA. My guess is the former. If the latter, I would suggest a different overall route if time permits. It would be the TA to West Yellowstone, then the Parks, Peaks, and Prairie Route to Reliance, ND, where you break off and take a route I can get you to Milwaukee. About 90% of the route in Wisconsin is on rail trails. From Milwaukee, cross Lake Michigan and then head south on the North Lakes to the alternate (south) Chicago to NYC Route to Philly. The reason is it has much more scenery and varied terrain. You would definitely want to start at least mid-May as Yellowstone can be quite cold in June. I rode in a wet snow on July 4 back in 80s and it was not super fun and I started in Astoria in early June.
But if your time, dates, miles, etc. prevent that, I totally understand. I don't think your route is bad at all, just that my proposed route is much more scenic.
Wishing you a wonderful tour! Tailwinds, John