I am ... who ... Generally speaking, the ways that you offer to ...are quite good; however, I have some better suggestions for you.
Firstly, it would be greatly appreciated if you could ..., because ...; Moreover, 原因, so it is advisable for you to put emphasis on ...
I hope that you will find these suggestions helpful .
I am ... who ... I am writing to make a complaint about ...
具体事由. To resolve the problem, it is advisable for you to 方案一（+原因）.
I hope that my problem will get your kind consideration.
Dear Sir or Madam,
I am ... who... I am writing this letter to inquire some information about ...
First, it would be greatly appreciated if you could let me know ... , because ...自身需求. Second, since 自身需求，I would be very grateful if you could send me relevant information.
I am looking forward to a favorable reply at your earliest convenience.