Steve, congrats on your purchase of a TM WH and TIR. You might want to look at getting some TM Cougar MFDs and a rudder pedal set... I have a Saitek Pro Flight set (£99) and they work fine. The MFDs are optional (less reaching for the mouse) but the rudders are essential

Above the DCS A10 forums are two sub-forums on Training and FAQs, I suggest starting there. I have a newbie guide that will orient you to the essential bits of the cockpit and Sim has a picture-guide on how to make things explode. The sim itself has very good tutorial missions so do them but don't worry if you don't absorb everything on the first go, just take notes. Wags'
YouTube section has some really good stuff as well.
Make sure you have the latest version of the game installed, which is 1.1.1.1. If you bought your game elsewhere (Steam, boxed version, etc.), your keys will work with the DCS download so get the
latest version here and input your CD key when asked.
When you get your TM WH, you will want to un-map the view control from the joystick's Trim hat (the gray-colored hat) since you will have TIR for your view control. Now re-map that Trim hat to the trim functions.
That should be enough to get you started. I would suggest starting with learning how to start up the aircraft, if nothing but to know where most of the switches are. Then move on to take off, navigation, and landing. Then on to the fun stuff -- making things explode, burn, or run away.
Good luck!