starting over

[Grod1]

I have been brewing 1-10 gallon batch for a couple years now, but everything is simple and strait forward. I am about to dive into 1 barrel batches and its going to be a little bit harder. This is my plan to get 40 gallons.In the same amount of time as a 5 gallon batch Using a bit more then twice the equipment.
3- 20 gallon kettles /3 burners/2 mashtuns/1 barrel fermenter

Batch Size: 39.5 gallons (fermentor volume)
Original Gravity: 1.045
Final Gravity: 1.002
ABV (standard): 5.59%
IBU (tinseth): 10.77
SRM (morey): 4.85
FERMENTABLES:
20 lb - American - Pale 2-Row (32.3%)
12 lb - Dry Malt Extract - Wheat (19.4%)
6 lb - United Kingdom - Maris Otter Pale (9.7%)
5.25 lb - Pear (8.5%)
4.125 lb - Grape (6.7%)
4 lb - German - CaraRed (6.5%)
1.5 lb - Flaked Corn (2.4%)
1.5 lb - Flaked Wheat (2.4%)
1.5 lb - American - Aromatic Malt (2.4%)
6 lb - Honey (9.7%)

HOPS:
1 oz - Hallertau, 50 min, IBU: 1.8
3 oz - Styrian Goldings, 50 min, IBU: 7.63
1.5 oz - Hallertau , 5 min, IBU: 0.54
1.5 oz - Styrian Goldings, 5 min, IBU: 0.8

YEAST:
Bootleg Biology ; Sour Solera Blend with dregs

To start the day we will
-bring are strike water up --40.6 gallon.
-Along with starting a 13 gallons boil.The strike water will be split into two mashtuns target mash temp in one being 150F target temp in the other 158-160.so that half the wort is highly fermentable and half is long chain.
-add wdme and honey to 13 gallon boil and collect 12.5 gallons of 1.067 wort. chill and transfer to fermenter.
-collects 24 gallons from mashtuns and boil down to 20 gallons of 1.048 wort. while this is coming up to a boil
-add 4.5 gallons to each mashtun and collect an additional 7.5 gallons
this step can be omitted by adding 7.5 gallons of bottled water(?) since there wont be much sugar.
-pour "pear halves in white grape juice directly into fermentor from un opened jars .(half gallon of volume)

 

[Grod1]

Ok so my questions are:
Would you split the hops between the two boils or would you put it in to one batch?
How much water can fit into a igloo mashtun after its filled with grain?
How do i figure out how much of my own yeast to add?
Would you add bottled water to fill up the headspace (7.5 gallons) or do a combined batch sparge of the two mashtuns to pull out the rest of the sugars(>1.010) and boil?
Is there any problems that i might run into blending the 3 or 4 boils together that im not thinking about?