I was going to mention saddle height. A decent place to start with that is you should just be able to reach the pedal with your heel, without rocking your hips. When you are pedaling on the balls of your feet (as you should be) you should still have a slight bend in your knees.

Pretty much any saddle will probably take some getting used to, if you haven't been riding much. But there is a difference between having your butt get a little sore and feeling numbness. The latter would suggest your saddle nose should come back down a smidge. It can take a few rides and many tiny adjustments to get it just right. I am often amazed at how an adjustment of a couple mm in saddle height or angle can make a noticeable improvement in fit and comfort, which just compounds the farther you ride.