Some recommendations from my side:
Mast lengths: I have several diy foils with aluminium masts between 65 and 95cm - for chopy conditions I find the 85cm the best compromise.
95cm is too long: Difficult to get on foil and quite flexible.
Battery: I basically use different batteries for all my builds.
Worst experience I had with the original Samsung 18650 which showed significant drift even after the first year - but even after 6 years they are still useable.
My favored battery so far are the LG M50LT cells - cheap, plenty of capacity and no drift even after 3 years - same cell I have in my Tesla 
However, for my next build I will use a higher capacity version from LG, Lishen or EVE. In my experience with an 8p or larger battery everything above 10A discharge is ok.
If long range is your priority I would go with the new Molicell or EVE 6Ah 21700 batteries.
Otherwise I would recommend to trust ludwig_bre - he has lots of experience and is always reliable in his advice!
Thanks I Appreciate your input. I was swinging towards the molicell but will look into Lg.
@ludwig_bre is this the bms you where recommending?
https://amzn.eu/d/07Sdblhp
How high is the motor normally placed above the front wing the diameter of the prop is 153mm?
How is everyone dealing with foil mounting having fish bones for foil adjustment would be nice but then how do you deal with cable slack if I have used epoxy to seal the cables to board?
Definitely not recommending any of the BMS haha 
This is the one I have
https://de.aliexpress.com/item/1005012471464165.html
But again, would not trust it with my life
I place it as low as possible, maybe 5 to 10mm gap to the fuselage
My motor cables are sealed with silicone on the top of the mast towards the mounting plate
No slack really, just enough to exchange the motor mount adapter
What you mean it don’t come with a 10 year Ludwig guarantee lol
That link ain’t working for me.
I heard someone call them fish bones but I think there actually called rail mounts or box would be nice to have mast adjustment but it creates an issue with cable slack. Didn’t know people still used silicone haha get yourself some sika flex or epoxy for a proper seal.
This one came to mind:
Morning folks I wonder if this would work with a twin flipsky 75300 Kill Switch with 3 Independent Channels Stop Motor When Fall off from – Maytech.cn--Maytech official website
Looks like just a relay and a normal off the shelf pull cord kill switch
Should work with any receiver and ESC
From what I see it will steal 5V from the Rx for relay power
And with the relay forward or short-circuit the PWM signal used for communication between Rx and ESC
For your build all I can say for maximum reliability keep it simple. The best part is no part. Single oil filled motor, aluminium prop, over spec the vesc (like a makerX g300) with passive cooling, carry a spare remote.
For extra reliability a direct discharge battery is probably better, but via a BMS is quite reliable if the pack is made well, no bad welds which could cause shut down protection.
Most issue people have are with water getting into the system so spend 90% of the design effort make redundancies around that. Corrosion X and potting.
Thanks for your insight. I Agree with keeping it simple theres a reason the Ak47 is the most common gun in the world simplicity and reliability. Currently trying to get some board inspiration and design the shape is there a software anyone recommends? I like the idea of the board having a dugout with a point nose/raised wave breaker nose a flat deck at the stern and a gunwale. Some images I like and yes I understand some are paddle boards and are far too long I am purely look at shape
Its no cad drawing but it works. Getting pretty close with side profile I want. The board will have double thickness on the flared nose and a small gunwale on the deck with an open stern considering placing one battery pack behind the mast for better balance.
Always open for new Ideas.
But your complete idea is a non foiling design.
It is even a non planing design.
Considering you use a motor, that makes exactly zero sense to me.
Your nose is just dead weight you are driving around.
You want the weight above the front wing, which is usually forward of the mast by quite a bit, so the battery should also be placed there
Ah sorry now I understood, 1 battery pack front, one aft…
If possible I would place both front, with the center between the packs above the center of lift (close to the front wing)
But yeah if that’s not possible one behind may make more sense…
Clearly not open to different design and it ain’t new @Jan12 if you haven’t got anything positive or actually factul to add just wheesht! You go watch any beginners whats there main problem nose diving. Take the shape compare to majority offshore boats its pretty identical and if they can’t plain that would be strange lol. The aim of the board is to maintain speed in ruff conditions https://youtu.be/qQzdAsjWGPg
If you post here, you also have to accept negative comments. If you already know everything, why post here?
I think it saves a lot of time, money, and trouble to listen to the collective intelligence of this forum. Why make the same mistakes that other people already made years ago?
Of course, thinking outside the box and being open to new ideas can lead to innovative products. But there are designs that have proven to work, and others that have already failed.
For your battery, I’d suggest making it modular so you can use either one 2 kWh battery or two. Your setup will get really heavy—it’s no fun carrying 40 kg to the shore. About 30 kg is my limit, and I wish my setup weighed only 25 kg.
Look lad I clearly don’t now everything otherwise I wouldnt be here! 10 years of efoil intelligence is not alot compared to how many thousands years of boating intelligence. Just posting my plans you want to bash be prepared to be bashed back its that simple. The biggest problem is here is people not reading before posting for example if you read somewhere above I have already had the modular idea! On the first occasion of bumping heads here same again not reading and jumping to conclusions. I will pick and choose the advice I want not going to jump off a cliff cause 3 people say so. As for you wanting a lighter board you know what they say grab a teaspoon of cement mix in your tea and harden up lol
Says the one with 6h spent reading the forum…
Caught with your pants down ans still don’t quit while your ahead I suppose you expect me to apologise for having a life. You lot clearly forgot the history of the hydrofoil and tell me how many are flat bottom hulls you ever been on one of the old soviet hydrofoils if you haven’t you should really cool 
Switched from muted to ignore forever, soviets have had better times, looong time ago…