Wangfujing is what I consider central vs Beijing West which is on the "near west" side. Before 7:30 am traffic from former to latter is not bad. But at any rate, you've found your hotel.

If you need to be in Shijiazhuang by a specific time, which then narrows your specific train departures, you should have hotel concierge get the ticket day before. If you have a bit of flexibility (say arrival target range covering 3-4 hours), then you can probably do as a walk-up for next available train. Normally cut-off time for sales is 30 minutes before scheduled departure, and your passport # will be needed. I don't recommend this for rookies though, as BJ West station ticket queues can be formidable at all hours. If you have a partial day in Beijing the day before, the hotel can point you to the closest remote ticketing office, where queues are minimal, and purchase is quick and easy. RMB 5 surcharge for remote ticket purchase, and take your passport.

Finally: make sure you know where you want to end up: Shijiazhuang (main) or Shijiazhuang North station, in case it matters. The first 6 trains leaving between 7:00 and 8:40 are the D123, D2001, D137, D4561, D2003, and D121. The D2001 and D2003 got to North station, the others go to main. All are under 2.5 hours. Go for the first class seats since the premium over second class is negligible.