I wouldn't try to automatically use a capitalized "SMTP" as in the example you "had tried" at the end of your post. If you did then every entry you add in to a proxyAddress attribute would have a capitalized SMTP. Only the main login should have capital SMPT, the rest of them (aliases) should be lower case).
As for improving PowerShell skills, I bought this when it was released: https://www.amazon.com/Windows-PowerShell-Step-3rd/dp/0735675112
and I highly recommend it. I haven't gotten though much of it yet because I'm trying to finish up some MCSE's first, but I will be diving a lot more into it soon.