Hi,

You can see a larger thickness set in LineChart sample project like this -

lineChart.Plot.SeriesStyle = new MixedSeriesStyle()
{
    ....
    UniformStrokeThickness = 5
}; 

Note that if you have assigned a SeriesStyle to either separate series or the Plot, this will have higher priority than values you assign to the chart.Theme.

It seems we don't have direct properties to customize the scatter shape and size in line charts. You can specify them like this instead -

lineChart.ShowScatter = true;
var scatterRenderer = lineChart.Plot.
    SeriesRenderers.OfType<ScatterRenderer>().FirstOrDefault();
if (scatterRenderer != null)
{
    scatterRenderer.Shape = ScatterType.Diamond;
    scatterRenderer.ShapeSize = 20;
} 

Regards,
Slavcho