Hello, my name is Alisha and I have been professionally writing for 8 years. In addition, I have been working in the marketing and advertising industry as well. I read your requirements and think that the 3 letters you mention are indeed crucial, however there are a few other aspects I would also look at and some questions to appropriately address your requirements. Please find my elaborations below:
1. Will the letters will be sent electronically or as snail mail as well?
2. Letter 1 - I will add the expected time frame for completion of the job and possibly the size of the team. Suggest to keep the writing short and simple and perhaps use info graphics to communicate much of this info. Would also include links to all social media accounts and inform them that they can find updates there.
3. On the social media accounts- announce in which areas (not too specifically) we are working and give regular project updates. The span of the updates depends on average project span but should be kept consistent.
4. Before letter 2, somehow contact them on the day before the project commences, perhaps in letter 1 they can have the option to opt-in to this as a reminder service.
5. Letter 2 I agree with inviting them to see the completed work, again also add social media channels and do the updates of the project on social media.
6. Letter 3 - I would change the angle from apologizing to the car wash.
I have reached the character limit, but will gladly discuss more.
Best regards
Alisha