Does dupuytren's affect your thumb and ability to flex your wist?

Yes. Depends on location. There are a variety of treatments available if necessary.
Yes and no. you can get a cord that affects the movement of your thumb but the wrist is not usually affected in dupuytren's.
Thumb yes. It is unlikely that dupuytrens would affect the wrist. It can affect the thumb. There are 3 options for treatment of dupuytren's contracture: 1) fasciectomy 2) needle aponeurotomy - see my article in journal of hand surgery april 2012 3) xiaflex the treatment chosen will depend on the location and severity of the cords.
WHile it can affect . Your thumb it does not typocally affect your wrist flexion. It can affect wrist extensoin but not by a cord in the wrist but the tight palm or finger cord can be and feel tighter with the wrist extended and the palm skin under tension. Rarely knuckle pads on the fingers make the fingers and perhaps if severe wrist flexion is affected but not usually.
I can . Dupuytren's can affect the thumb but is less common. I never affects the wrist. Most common fingers affected is the ring and little.