Hand built cars always need some sort of sorting. Screw ups and surprises, can and will happen.
Everyone use to buy Tuesday to Thursdays cars and never Mondays from Detroit have we forgotten this?
The fact that someone is living so far away from the builder does not help the situation and chasing a gremlin can be no fun especially when you find a hose end like Jim found in his Coupe cooling system or in your case with the carbs. Or your building what amounts to be a prototype of a new build for the builder.
Sorting my car provided some agony, some fun and frustration and cost, but human error will occur I am not sure that venting on this forum helps at all even if your life was put at risk by an error in building.
You signed up for a hand built car with all the risks and you rolled the dice. Some would say your crazy to build a handbuilt car and take those risks why not just go out and buy a brand new 911 and they do have a point.
Are you unhappy with the journey? Well, maybe and maybe it is because your at the top end of the scale for build costs you are maybe even more frustrated but venting here without a possibility of any comments from the other side is fruitless IMO.
In any case, my car is sorted and I love my IM, it is a great car and it has had and has it's nuances/ issues being hand built.
I have owned 50 cars in my lifetime, have I lived that long 
Some I got rid of because they were lemons some I did not like and some were just DDrivers along the way.
I hope your car is finally sorted and that the experience in the end will be more enjoyable and bearable for you... just remember, in the end you can always sell your car. Welcome again to the madness.