Congrats on the new bike! I saw a prior thread where you were weighing your options. I think you made a shrewd choice. and I hope it serves you well. As for the stem, to reiterate what others have said, stem size is determined by your body proportions. Nitto Technomic stems would be a nice option for a quality Japanese models, and can found for reasonable prices (several in the mid-$30 and lower range on the 'bay).

Btw, I was in Seattle recently on vacation & walked into a nice LBS in the Belltown district of Seattle called Belltown Pull-apart: http://belltownpullapart.com/. THey had some nice bins of used vintage parts for sale. It might be worth checking out if you haven't already.

I hope you find cycling is not too painful on your joints. If you do have discomfort, you might consider even more padding on the handlebar tape. There is a famous one-day "classic" race called the Paris-Roubaixwhich includes sections of bone-jarring cobblestones. Riders frequently double-wrapped their bars with cork handlebar tape. There is also this new (albeit pricey) cork tape with gel coming out from Cinelli, available later this month.