MY LETTER: 

Dear Manager,

I am an employee of DNDD Corporation. We are considering buying 200 CS900 workstations and 100 DP540 servers from your company. So I am writing to request some information related to your company’s services.

First, the branch of our company that needs the computers is located in No.18, Nanjing Road, Shanghai. I would like to ask how much we need to pay for the delivery from your nearest branch. Second, I would like to know the warranty period for each of the components of the computers. Can you send me a detailed list? In addition, in case something goes wrong, will you send someone to repair the computers? Finally, I would like to ask for a discount. According to our current budget, an 80% discount will allow us to buy 100 more workstations and 50 more servers from you. Besides, we would suggest DNVD buy some computers as well. Is the discount possible?

We are looking forward to your early reply. Thank you.

Yours sincerely,
Nelson Lee

Everything is grammatically correct. But, those 2 sentences I would change. 

1. "Besides, we would suggest DNVD buy some computerrs as well." 

This is just my opionion to be honest, but I think if you worded it a little different it would sound more professional.

2. "We are looking forward to your early reply."

This is technically correct, but no one would really say this. There are many different ways you could word this, but even saying, "We are looking forward to your reply." I think is better.