LineChartAppearance lineApp = this.ultraChart1.CompositeChart.ChartLayers[1].ChartTypeAppearance as LineChartAppearance;
lineApp.LineAppearances.Add(new LineAppearance());
lineApp.LineAppearances[1].IconAppearance.Icon = SymbolIcon.Circle;
lineApp.LineAppearances[1].IconAppearance.IconSize = SymbolIconSize.Large;

that should answer your first question.  as for the second one ... you can either use the axis Margins for the x-axis of the line chart, or you can handle the FillSceneGraph event, find your Polyline, loop through its datapoints, and re-map them using the x-axis.  that would look something like this...

ChartLayer columnLayer = this.ultraChart1.CompositeChart.ChartLayers[0].ChartLayer;
            Axis xAxis = columnLayer.Grid["X"] as Axis;
            foreach (Primitive p in e.SceneGraph)
            {
                Polyline pL = p as Polyline;
                if (pL != null)
                {
                    for (int current = 0; current < pL.points.Length; current++)
                    {
                        pL.points[current].point.X = (int)xAxis.Map(current + 0.5);
                    }
                }
            }