The areas in the bar are too small, and so the labels wouldn't fit - that's why they were omitted. If you're using my cewolf distribution (see my signature) then you can use the AnnotationProcessor chart postprocessor to add labels outside the bar; you'd have to do some experimentation to find out for which values the "internal" labels are not displayed, so that you can set annotations for those.
The example web app that comes with my distribution has an example of how to use the AnnotationProcessor.
#1: The bars are sized according to the values they represent and the overall chart size. I assume you don't have any influence on the actual values, so increasing the chart size would be the only option.
#2: Again, the larger the chart, the bigger the space between the bars. You can also play with the itemMargin attribute of the BarRendererProcessor postprocessor in my distribution.
What do you mean by "the interval"? The difference between adjacent label values? That, too, is dependent on the actual values so that they appear neither too cramped nor too sparse. You could write a postprocessor that sets a different TickUnitSource for the range axis, though.
for few bars it not displaying the labels though the space is available to display the numbers.
It would seem that the library has a different idea of what "enough available space" is, so the answer in my previous post applies.
By the way, you can make things easier for anyone reading this post by using an image format that is displayed in browsers, like GIF, JPEG or PNG.