The leash will fit the Jumbo just fine.

The Flight Suit is not meant to be left on the bird unattended.

Once the suit is on the bird, you may need to distract it with a treat, a walk around your home for a bit then take the suit off and reward your bird again, this may need to be repeated a few times before the bird realizes it is not a permanent outfit, then it it would for sure try to remove it.

Once it realizes it gets to go more places or be with you longer while wearing it, there will be less fretting about it.

Birds are not used to having to wear anything.

Learn more about flight suits for birds here