2 hooks are pretty easy, because as long as you put load on both hooks you spread the stress evenly, the 3rd hook is the tough one. Two outer hooks, roughly in line with or slightly outboard of the loader arms are pretty common.
You didn't ask about it, but if a center hook is installed it can collapse the center of the bucket lip on some bucket designs. Not sure about your bucket, but the bucket of the Kubota
B3030 at my local dealer does not have a reinforced top lip, it simply has a double fold to make a squared off "C" shape. That is a pretty strong shape, but not as strong as if there is a square tube welded under the upper lip. Some folks weld in angle iron to reinforce the upper lip, that works well too if the upper bucket lip is not reinforced.
About 2 weeks ago I ran a thread that compared a lot of different tractors. None of the Kubota buckets on that thread had what would be defined as a H.D. bucket with a reinforced upper lip. I posted pictures of an
L3400,
B3030,
B2910 (mine) and
B7800. All 4 had somewhat similar buckets, all had top lips with "double" folds.
Interestinly there was no consensus between brands and how the manufacturers built buckets. NH had round and square tubes under the top lips. Branson had a "single" fold. John Deere had either "tubular" rolls or "double" folds on their standard buckets, but their optional HD buckets were substantially reinforced on all 4 sides of the bucket perimeter. Montana had "single" folds.
I guess some of it might be cost. Some of it might be calculated risk as most owners probably don't put hook on their upper bucket lips so an upper reinforcement might be an unnecessary cost 80% of the time?