To answer you first question, you need to set up a calculation that identifies few starting and closing months and use this calculation to display those desired labels.
In case you want exact values on X-axis then try using discrete date field. With existing set up you have to edit the x-axis range until you get the desired result.
Thanks for your reply Tushar.
So what you do mean by that identifies few starting and closing months.
Can you provide an example.