Here's a Slate story about a Kickstarter hardware project that failed spectacularly. The income Kickstarter generated was counterfeit, because the guy running the business was swamped by expenses he hadn't predicted out the outset and would only learn when he needed to ship in volume. Spoiler: all he was trying to sell was lockpicks, little shims of metal.
http://hive.slate.com/hive/made-america-how-reinvent-america...
Want another example? How about Wakemate?
Good business people will anticipate the expenses needed and make sure there's a way to pay them (or delay payments and make sure everything is in a company with limited liability), borrow money in the bank with collateral in your inventory, get good deals with suppliers (If you do it right you'll get a 90 days credit line thus nullifying much of your cashflow problem), etc. etc.
The article discusses how this guy abandoned his friends, launched their project without them, then went money-crazy when the project was funded. This guy is spending on conferences, unlimited air passes, and $24,000 worth of locks and Open Locksport swag, but doesn't even have a source for the lock picks he's "sold" to people.
Maybe the best part is where he has to spend $2000 to hire a go-between to talk to lockpick suppliers, as he was too insecure to do so himself. Maybe one of his friends could have done that, if he hadn't abandoned them. No...the best part is where all the conferences and flying and vacations has caused him to become depressed, so he checks himself into a hospital. sigh
Oh, and I think the friends he abandoned came back to sell his locks and sell this story. I'm not completely sure if they're his friends, because the Slate article is very unclear about this.
Cost of inventory is an issue, but there are several ways around it, including dropshipping and createing on demand. You can hire an MBA to optimize in this area (this is the area where they are supposed to do well).
Basically if you could honestly imagine your product doing well on kickstarter, you don't need to worry about margins.
If you can imagine your customers being willing to wait 3 weeks on the product you don't have to worry too much about inventory.
I very much doubt that YC will back a new factory to produce hardware for others.
I very much believe that YC will back a company that produces an alarm clock that makes you want to start the day, or a device to insert into your toilet that will analyze your urin and tell you if the measurements are out of whack.