Gabriel: Welcome to the forum. I haven't paddled below Emlenton but my understanding is that it gets tough downstream of Parker. The river downstream will require you to portage around or navigate through the Army Corps locks and there is little, if any, public land available for camping so you'd have to arrange something with the individual landowners (or trespass). As far as I'm aware, the state water trail ends at Emlenton for that reason.
If you want a longer trip than the (typically) 4 days from Kinzua to Emlenton, it would be logistically easier to start at Port Allegheny, paddle the upper Allegheny, portage around Kinzua dam & continue downstream to Parker or Emlenton. There's not a ton of camping above Kinzua either and this plan would require you to paddle a lake that is overrun by recreational boat traffic in the summer but, if you picked your season, you might not get run over.