Hi cron,
As far as handling goes just be patient with her. Carpets, like many other snakes, can be a little nippy when they're young but most of them grow out of it pretty quickly. If she's a little too bitey I'd use gloves to lift her out of her enclosure and then take them off once she calms down. Get a few more meals in her, let her acclimate to her new home, and she should chill out. I would also suggest hook training her now. Carpets can be pretty food driven and will strike at the first heat signal they sense when their enclosures are opened. Once you rub or tap them with the hook they're usually much easier to handle. I ordered my hook from reptile basics.
http://www.reptilebasics.com/hooks-and-tongs/
The T-12 is a good cage. I'd order the divider and keep her on one side until she gets bigger but as long as she has plenty of hides and floor covering there's no problem with putting her in an adult sized enclosure. Keep us posted on your progress and share pics when you can.