Rebel Hog gave you a good chart on the size and # of pellets in the shells.I have always shot buckshot for deer and hogs till I got a place that I stand hunt with a rifle.
I hunted in the Fla. swamps for the past 42 years and I say 35 was only with shotgun and buckshot.buckshot in my BPS 3" with Winchester #4 buck have taken over 140 deer and twice that many hogs.I always took shots that were 50 yards and under(mainly because in the swamps,thats as far as you can see and tell what it is)I used # 4 buck because we had so many turkeys.then I foundout they took deer and hogs great.
I had an uncle put it this way to me once.he said take an orange and a grapefruit; throw them both as hard and as far as you can.he then said which one went the fatherest,I said the orange,but the grapefruit hits harder.he said yep ; if it get to ya.just something to think about.thats why I shoot #4 buck.

back to the buckshot,I would get some #4 ; some #1 and the 00 you have.take a 1/2 sheet of news paper and put themat 30 and 50 yards one behind the other lined up so you only see one sheet.shoot them and you will get an idea of how you gun shoots.the newspaper want make a difference in the pattern.try that with each different shot size to see which one does the best.

as for the shot placement; I would try for a broadside shot,that will most times drop them.I have only had 2 or 3 deer that ran off after I shot them,all the rest dropped.a head shot is iffy at best;small kill zone and will distroy the rack to boot.I took a shot at one buck one time that two other hunters had shot with arifle and both hit him;one was in the front leg justabove where the knee was; the other was just below the spine.he was running ahead of a pack of beagles.I shot him at about 75 yards(only shot that far because we knew he was wounded); he dropped in his tracks.hit himwith 3 in the lungs and 2 in the neck.

if you have him head on,just be ready for the turn and fire;(DEAD DEER).

don't know if any of this will help you any; just the way I have used them over the years.

some people will disagree with me on this ; But There Wrong[8D]LOL