1) Unless you are using 5 gal buckets the 6" is prob what your gonna find. When using the 5 gal buckets the "Bucket Basket" can go up to 10" I know for sure but thought I saw 12" at one time. Size of the basket pertains to how tall your gonna grow.
2)Weekly is what I always did but you can go by the process of when your topoff amounts equal what your res started at.
3)You should not really ever have to lift the lid completely off if all goes right. Most of the weight of the plant is in the water below your Media.