Even though you don't know the count of the bars you can use the maximal value of the chart Bars and set it as MaxValue of the XAxis. To be able to do this you should turn off the XAxis.AutoScale proeprty
and provide your own values for MinValue, MaxValue and Step
. This way, you will always have the same number of items along the X axis, so the bar will always be with the same width.
Setting custom scale with appropriate Step will help you resolving your second issue too.
All the best,
the Telerik team