If you want to avoid the hills and mountains you could ride south thru NJ to MD's Eastern shore and on to Washington DC. There pick up the C&O/GAP Trail which will land you in Pittsburgh on the other side of the most serious terrain. It's round about but depending on your conditioning it beats walking up hills for days on end.

Be aware that no place is really flat. And places we think of as flat could be anything but. SE Ohio for instance. It's got some killer hills.

Staying away from bad areas is going to take some research. Once you've pinned down your route take a look at the major cities and towns on the route. Something as easy as a google search could get you what you need to know. Or, a call to the local PD. It all goes into the trip planning folder.