Conditional forms and disabling input fields?

I'm working on some forms that I see as complex.

Step 1: 3 radio buttons (a, b, c)
Step 2: 2 radio buttons (yes, no)
Step 3: input fields, amount varies based on the combination of step 1 & step 2 selections. Step 4-6: not required, non-conditional.

If I select "a", "b" or "c" in step 1, and then select "no" in step 2, i don't see step 3.
If i select "a" in step 1 and then select "yes" in step 2, i see 3 input fields in step 3.
If I select "b" in step 1 and then select "yes" in step 2, i see 5 input fields in step 3.
If I select "c" in step 1 and then select "yes" in step 2, i see 1 input field in step 3.

What is best practice for loading conditional inputs on page load? Should the input fields be disabled until the pre-conditions are met? If it's disabled, what does step 3 look like on page load (meaning, what input fields are displayed -- 3, 5, 1)?