Physical Product Design: is there guidance/books on how to focus on only the most essential features that deliver the most value? (80/20...)

If you're talking about an app-store launch, then it's important to have the core mechanics of the product (from a user interaction perspective) figured out such that the majority of your users are doing the things you want them to do in order to drive continual engagement with the app. Design polish can come later and often slows down whomever is implementing the development of the app. I don't think anything should ever be "ugly" but lacking polish is often the right way to go to get speed to market. That said, to be sure of the core interactions, you want to do as much testing and observing real users use your app prior to launch. Happy to talk through any of this in a call with you.

Shipping components are expensive and unless you have the volume to buy in quantity vs small bundles is when you'll be able to shop around for a better deal. For example, Uline offers packaging in bundles of 8 or 25 as their minimum, this is stock item for which they order several thousands units of to keep the cost down. For you it fits because you can buy in small amounts at a time. However, if you have a need for 1000 at least or more units then buying from Uline is really expensive compared to what you could buy them for. Uline is a major distributor with a 45-50% markup on their items (give or take) as they have large warehousing and infrastructures. If you are ready to move to the next level, first find the correct material name for each packaging component, and look for suppliers of that particular item. Search websites likehttp://www.thomasnet.com/ for suppliers. Or go through a packaging broker instead of a distributor, like Landsberg Orora, or Ernest Packaging, and they can do all the leg work for you and still save money. Additionally, I know your drawing is not to scale, but there seems to be excess empty air space, if that is true then you can customize your packaging per exactly your needs, which will help to further bring the cost down. An engineer should take a look at your current situation because there is more at play than just shipping components - method of shipping, weight, weather condition, materials thickness etc all play a roll and can all contribute to cost saving while making the whole thing function better. This question is common enough that I've written tutorials on it http://howtobuypackaging.com/how-to-buy-packaging-part-1-determining-your-packaging-needs/.

I have built several multi-million dollar businesses using (2) very simple questions: "What makes you say that...." and "Tell me more...." No matter what someone says to you, you just keep asking one (or both) of the questions. If you do it 4 or 5 times in a row you'll learn everything you ever wanted to know.

It varies and it's very very specific to what you want to develop. The concrete design of your circuit matters. Also prototype building costs are usually a factor 10-100 higher than series. If you already have your prototype then you can shop around various manufacturing companies. To do that, you need Gerber files (your PCB design) and a bill of materials. You also need to think about casing: designing it and creating the mold is expensive. If you don't have your prototype yet, I recommend having it engineered in eastern Europe. Custom engineering is cheap there and high quality. IP protection is a problem. One thing to do is to distribute the work to different manufacturers. For the design phase you are safer if you design your prototype in Europe or the US where international patent laws apply. I could give you more specific advise in a phone call, getting to know a bit better what you are trying to build.

This is a great question and an important one as well. I would start by identifying: Who is your target market? How will they use your product? On the go? On their laptop or on their mobile device? What kind of technology does your product need? Can it be built as a simple website or does in need to be an app (i.e. you need push notifications, integration with other mobile apps, etc). On the other hand, how much time and budget do you have? Typically a responsive website is faster and cheaper to build than an app and will get you out the door faster.