Hey I did the first quest (above) in my current character, and then went off and completed the thieves guild line. That took me forever as I did lots of side jobs and I am concerned that even now I have not recieved the second letter from the Solitude Steward. Is there something I have to do to prompt him to send it?

You have to be at least 10th level to start the second Potema quest. It could be you are not that high yet?

You also have to level up once.