I would drop “sir” and just keep it at “Hello”. There is no need to repeat the whole request when mentioning that you saw their request, because you are already replying to it, so they know what you are applying for. You can just start by saying that you saw their request and you can definitely help them. In the next sentence you can include what exactly you can do for them (include what they asked for, and, if it’s the case, maybe some additional related services).
Then you mention your experience and other assets. Letting them know samples of your work are available on your gig is good and can be convincing.
I second the fact that offering unlimited revisions is not a good idea (you can end up revising the same order 50 times, while the buyer might interpret it that you are not confident enough of your skills and that your work may lack high quality).