PVC drain

Hey guys....looking for a little clarification on a problem I had posted earlier.

We moved into our house about 9 months ago. In a basement closet (about 7' X 2'), the previous owners had a pump installed. The closet is underneath the front porch, so it is exposed to an outside wall...and we are in PA, so get pretty cold during the winter.

From the pump, 1 1/4" PVC pipe extends up the side wall about 4 feet, to the outside. Currently, the pipe is diverted away from the house, but not the entire length of the front yard (about 25 feet)...probably about 3'...so when the pump discharges, mud from a flower bed (behind a stone wall) erodes all over the driveway, leaving a nice mess after the rain stops.

I'd like to take care of this in the next couple months. But still have a couple questions.

Is it OK to continue to use the same 1 1/4" pipe? A few of the other houses around us have 4" pipe (extended all the way to the street, so I don't think I'll be breaking any code by extending, and draining, into the street, as plenty of houses in the area already have this...PA is famous for basement water). If I do upgrade to 4", how does that work? Are there fittings made to handle this?

Secondly, I've read about venting the pipe, to avoid freezing in the line...how does that work...and is it complicated, or is it something a somewhat handy, but no expert, would be able to handle?

Thanks for all the advice guys.