Hehe... I read some trepidation in your blog about bringing home the new guy. I'll bet you $20 s/he'll win you over faster than you expect... a lot of us have been, or live with people who at first weren't too thrilled with the idea of a rat, and now they're devoted rat lovers.
As for rats being diurnal... I hate to be the one to bring it up, but probably in all the activity at the school, the little guy couldn't sleep, and so learned to stay awake. As time goes by, don't be surprised to see him sleeping more during the day and staying awake at night.
That said, I sleep in a small room with my rats, and as long as their wheel is kept oiled (vegetable oil is my new best friend) and I don't make the mistake of giving them a noisy new toy (i.e. a piece of paper to tear up) before bed, they're actually really pretty quiet, so I wouldn't worry too much.
And yes, you'd have a much happier pet if you could go grab one of her sister for her to play with... two isn't any more work to take care of than one, and they'll keep each other (and you!) very entertained.