Not questioning your math or battery knowledge. 
however the 140A isn’t something that happens on a well configured efoil rig.
If the board has a reasonable volume and it and the foil are a good match for rider weight the takeoff happens very quickly. Once the board is out of the water the drag drops dramatically so “power usage” is briefly high and then levels out at a relatively lower level.
So on my planned 14s pack which is 50v I will need 120A to get 6000w max at takeoff. My VESC can take 240A. Guess I won’t need water cooling then? 
I searched for your board specs and came up with this
Assuming it’s the 11L board I think you are going to have a lot of trouble using it to efoil
You have approx 7kg of battery and 3kg of motor plus the weight of the foil and other items required so not much for body weight.
I weigh 85kg and use a 100l Fliteboard and while at standstill when I’m laying on it it’s about 1/2 submerged. Lots of volume to get up easily - can’t imagine the struggle to launch a board with 1/10 the volume!
I might be eating these words! I think that as long as you get some speed on the board the volume is not that important. I’ve made several wakeboards since the 90s, some out of plywood, some quite thick and floaty out of foam, epoxy and glassfiber. I dont notice much difference in time getting up. As soon as the tail of the board is releasing the water (bad Norwegian-English translation) and eventually planing the volume is of no use. If I lay down in the water, my body will float, the board will be submerged with the nose up. The speed will start to lift both the board and the foil will help.
But I’ll have to check if it will float in total 
Yes exactly. That is why I was keen to learn what sort of cruise power is needed. Comments above mentuon 1000w so at 43.2v is only just over 23 amps so not so much. (Ok this changes just using the nominal voltage x 12p pack)
Just need to design a system that can handle and stay with in the limits of the design. If the motor can draw 6000w 140 amps then the speed controllers and batteries need to be able to handle that. Likely will only be for 5-10 sec but still need to budget it in.
Will smaller S and higher P give more ride time?
Isn’t it the total watt-hours that matter? Higher S will theoretically give a higher max RPM on the motor. Also Higher voltage (s count) will need lower current to produce the same watts, and therefore generate less heat
@windego @Windigo @S_Roger , myself and others have built rigs that use the prebuilt 10S11P battery packs. My original thinking was to rebuild the pack to 12S but upon testing the 10S pack in my Fliteboard 100L, 65161 motor 75200 VESC, Fliteprop, Gong 1300 foil 85kg weight I was able to easily start and flat water Efoil, we all had similar design and use cases.
Yes it’s a good idea imo to overdesign the components within reason but in doing so you need to consider the “total” design and the use case.
In other words a light expert wave foiler would likely only need/want “small” “light” components, put the same rider on flat water efoil and they would likely want a bigger board, bigger battery (for range) etc. different prop (non folding) and a more capable VESC, different foil as they wouldn’t need to pump and so on.
There is a wide variety of build here, find one that comes close to what you want and model it, review the designs from Flite and Lift as they have this wired, take a lesson from a certified instructor that will likely have you up and foiling straight away…
I believe you are technically correct however my thinking is this.
The S count needs to align with “launch” and top speed requirements
The P count needs to align with range and weight/size requirements.
I personally like to get up on foil gradually so I lay on the floating board, get the board on plane on knees and then slowly stand, get my foot placement correct and then get up on foil. I foil at 25-30kmh even though the rig will exceed 40kmh as falling at 40 really hurts. I typically foil for about 10-15km and come to shore for a break and then quite often go back out for another lengthy ride all on the same battery
I’m using a 100L purpose built Fliteboard efoil platform and weigh 85kg and have developed some skill over several seasons. The 10S11P pack works for me but likely wouldn’t work for you - unless you were using my rig😀
My main thinking with the P count is just the max current draw from the batteries. If using the LGINR21700 then its only 15amp. Not sure I have seen any burst ratings for them. They would likely handle a bit of burst over the rating to get up on foil. Just over stressing the batteries shortens there life and they are the expensive bit.
When you say you are getting pre made batteries what part of the world is that in? Im in NZ and battery supply is limited and expensive. I travel to China often and could bring some back but limited to how many you can carry on the plane.
In terms of flight time I assume will be similar to when I was planing with quad copters. Its a balance between voltage and the KV motor you are using and the size and pitch of the prop. You need the motor to be running at its most efficent RPM. To acheive that you need the right S count and prop size and pitch.
I think motors are more efficent running faster. For max efficency maybe a bit diameter prop with low pitch to suit your cruise speed. But then that will kill your top speed and maybe torque to get up on foil.
If you have the option to try and few props would be intersting to see the results.
Lot of info on the battery pack here.
I Built 6 cell packs for efoils so far (12S & 14S; from 5p to 12p) - using Samsung, BAK, EVE and LG cells.
The LG 21700 M50LT are by far my favored cells so far - very affordable here in the EU, so excellent value for money as well.
Has anyone tried the Molicel 21700 P50B 5000 mah? They have a continious discharge of 45 amps which is fairly impressive.
Im going to pick up 8 and make a 4s 2p pack for more fishing quad to test them out. Currently using the panasonic 18650 4s 3p. They only have 10amp so 30amp total. The Molicel batteries are bigger but with a 4s 2p would give me 15% more capacity 3% lighter and would have 90 amp continious from 30 amp. The Quad only draws about 12-15 amps in normal flight but can draw 50 at full throttle.
So going to pick some up. Will do some cycles and capacity tests and see how they check out. The Panasonic ones were exactly as advertised and have lasted amazingly well. Hopefully these are the same.
If good will start getting some more together for the E foil project 
Cheers
When I ordered the bunch of 50s cells for my efoil build, I also ordered some p50b for my OneWheel Pint. I think they are a good choose for low P packs (mine is only 1).
If you compare it to a p45b it has almost the same discharge graph. But the extra 500mAh comes with a low voltage at the end. For my OneWheel I want the high discharge, but also the range, and having low performance at the end is OK for me.
But for low P batteries in power hungry applications like OneWheels and foil-assists you should also consider tabless cells. They have a lower internal resistance and will therefore generate less heat and can therefore push a lot of amps. Most of these are 4000mAh now but there are some like EVE 50pl that are 5000mAh. This one is hard to get your hands on now, and thats why I bought p50b.
Foil drive use the p50b for their HP packs.
I think FD use the cheaper Samsung 50S.
P50B is $6USD
50S is $2.5USD
Makes sense commercially I guess, but it’s not the best cell you can get.
50S only gets 200-300 cycles, Molicel gets 700-1400.
I can build a 11s3p pack with p50b for £250. The foil drive hp pack retails at £1059. Thats plenty of profit for them even with various other costs…
Paul at Foil Drive has confirmed that they are using the P50b cells.
Coming to think of it, they using 3P so the 50S would technically have enough current. Not a particularly great cell though. Did you strip one of their HP packs?
