I can put black paper around the tank to keep it dark.If you intend to keep the tank, make sure it is completely empty before moving it. If any water is left in it will slosh around during transport which will twist the tank and weaken the seams.
Fish in covered buckets is fine, you can even use something like old towels to cover the buckets.
Keep them in a darkish place for a while after you move them as they won't have seen the light for ages,.