Try sssigning the hem materials to the constrained cloth group and have the pants set to collide with the boots.

If you want to record an animation from say frames 1 to 30 you would need the cloth to be fully relaxed into position prior to frame one. This is where you would use the (pre)drape frames option. Generally 15 to 30 frames will be enough.

If you aim is to produce a pose for static render then I suggest that predraping the frames will not help much so just produce a simulation of about 30 frames. You may find that the "best" result occurs at frame 25 so you can scrub back to that for the render.

If you were to just use the drape frames option you would only be able to view the final result, not any intermediate frames.

Hope that helps :)