Well there are about 190 pages of Purple-Days Experience to answer your questions, this thread was started for 'availability' questions and for consumers to share shipping ETA knowledge.
I'll try to give a brief answer to them though.
You ask,"are ALL of the parts made individually? " That question would need definition.
I take basic off the shelf materials and 're-manufacture' most of them into new components. Our power jack, as simple as that item is, goes through a couple of modifications before it is used. I get vapor tubes as 8' rods and machine them to make tubes. Stainless tubing comes in 5-7 foot lengths and is worked in various ways. Kiln Dried American Cherry comes in big slabs... Etc. etc.
"how long did the design take to make"... It's an evolutionary thing. Always trying to improve, I am an inventor. How long? Read the story of the crossbar and how it enabled me to use stainless steel as a material. I think that was a key turning point in our design, and it took... only a moment. Other design changes were more deliberate, based on years of real experience in several industries that relate to this work.
How many iterations? Hard to say. The heart of the unit, the stainless steel heat exchanger, probably went through 5 or 6 prototypes, and two later changes, from 60 fins to 72 fins... then from shiny fins to Dark Fin Technology using black oxide finished stainless fins. But fins were in the design from day one. The body shape has evolved a bit, but round from day one. We have experimented with a several exotic woods that didn't work or are no longer available.
Every single Purple-Days has been built with RoHS compliant parts and Stainless Steel, never a compromise, since day one. It's why we decided to make our own vape.
So the answer is many, and one. Always toxin free. Always RoHS compliant.
Stop in on the PD Experience thread, lots of this stuff is covered, and lots more. Including why I do the things I do. I have always tried to be transparent and honest. We have an open shop and purchase records back to day one. You have to trust what you breathe through, and the people who make it. Don't you?