The email could have been pared down significantly. The idea that a programmer might want to solve problems directly rather than manage others should be well known at this point. The company I work for has an "individual contributor" career track for this reason. You can simply say it straight out without all the fluff, which is most of the email.
That aside, I'm happy it worked out and I understand it's hard to send an email like that.
> The company I work for has an "individual contributor" career track for this reason.
I once worked for a large information company that had a split between technical career paths (individual contributors to architects) and managerial career paths (individual contributor to manager to directors). So I stated in my HR profile that I aspire a technical career track to make sure, and told my management.
A few months on, I was sitting on a beach in Croatia during a vacation with my now-wife when my phone rang, and my boss told me I was promoted to Director. The reasoning was that the group I was leading would be taken more seriously if it was headed by someone who was himself at Director level, the same level as the peers that I would be doing projects for/with. Thankfully my team was small enough so I could stay reasonably technical, but I still envied the folks that "were allowed to write code every day" a bit.