Physics problem - Rotational Dynamics?

Ok, first, I'll give the problem, then my solutions and how I got stuck.... Be aware that this is a long question, though.

An green hoop with mass Mh = 2.6 kg and radius Rh = 0.12 m hangs from a string that goes over a blue solid disk pulley with mass Md = 2 kg and radius Rd = 0.09 m. The other end of the string is attached to a massless axel through the center of an orange sphere on a flat horizontal surface that rolls without slipping and has mass Ms = 4.2 kg and radius Rs = 0.19 m. The system is released from rest.

1)What is magnitude of the linear acceleration of the hoop?

2)What is magnitude of the linear acceleration of the sphere?

3)What is the magnitude of the angular acceleration of the disk pulley?

4)What is the magnitude of the angular acceleration of the sphere?

5)What is the tension in the string between the sphere and disk pulley?

6)What is the tension in the string between the hoop and disk pulley?

7)The green hoop falls a distance d = 1.68 m. (After being released from rest.)

How much time does the hoop take to fall 1.68 m?

8)What is the magnitude of the velocity of the green hoop after it has dropped 1.68 m?

9)What is the magnitude of the final angular speed of the orange sphere (after the green hoop has fallen the 1.68 m)?

Ok, so here's my approach:

1) I set up the system between the hoop and the pulley such that the torque is equal:

Rd*(Mh*a - T) = I*alpha, where I is (1/2)*Md*Rd^2

Rd*Mh*a - Rd*T = (1/2)*Md*Rd^2*(a/Rd)

The Rd's cancel out, leaving

Mh*a - T = (1/2)*Md*a

So now I have to find T. So I set a similar equation to the sphere and the pulley, giving me:

Rd*T = I*alpha, where I = (1/2)*Md*Rd^2

Solving for this gives me T = (1/2)*Md*a

However, plugging this back into the previous equation gives me that a = 0.... which can't be right....

So can someone tell me what I did wrong?

As for the rest of the 8 questions.... They're not difficult as long as I have the linear acceleration.

2) I'm assuming linear acceleration is the same for the whole system, so if I got the answer for #1, then it should be the same answer for this question.

3) It should be the linear acceleration divided by the radius of the disk/pulley due to the equation

a = alpha*R. Again, I need the answer from #1.

4) Same idea as #3, except using the radius of the sphere.

5) If I know the linear acceleration, then finding the tension using the equation from #1 shouldn't be bad.

6) I'm guessing same as #5. Correct me if I'm wrong.

7) Not so bad using linear kinematics. As long as I know the distance and linear acceleration.

8) Again, using linear kinematics like #7.

9) Using rotational kinematics, this question shouldn't be too bad.