Hello Yves
Yes, I have read your current letter and can understand why you believe that this content needs to be revised.
In my opinion you are attempting to CLOSE the deal before you have had a chance to SELL The Mail Center.
If I was given this assignment, that is what my goal would be. I would answer the potential clients question regarding price of course; but also list the services offered, background of your company. List the benefits of having you partner with them and then provide payment options. Perhaps a scenario or two of some of your clients situations; perhaps a testimonial of a pleased long term client. With communications going back and forth, my first draft, your comments and a second or final draft, I estimate that we could close this project within 3 hours at the very most.
I would engage the potential client before bombarding them with all the things THEY have to do. "We have a few documents for you to complete before we can begin serving you. Please download ....." I would certainly remove all that content up front.
I would also consider offering PayPal as a payment method for several reasons.
I am a semi-retired business consultant now living in the countryside, working from home. I maintain a mailbox in Ottawa, Canada, and have done so since 2008. So, besides being a wordsmith, I have experience being 'your' customer.
I hope to hear from you, and I wish you all the best growing your customer base, Regards, Wendy