Just a suggestion and not trying to be impertinent, but Japanese already has lots of "kimarimonku" (set phrases), so rather than trying to invent your own, why not just use the existing ones. For example,
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I would type out more of these but you can just look on a web site or an etiquette book and find lots more. For example, this website has phrases for business letters, or here are some ideas for books. There are lots more of these, I don't have specific recommendations.
(Thanks to naruto in the comments for the suggested phrase.)