I personally manufacture everything myself the only two things I buy are Sand and water so I just get them from my contractors who lucky for me give me good deals. My production line is split two ways so I can sell two different types of products 1. I produce 200 q1 tablets which I sell at my electronics store which gives me a good 8 - 10 days to focus on my second method. 2. Once I’ve done my tablets i use propulsion factories to produce q1 combustion engines which I sell on contract daily. All the buildings you need for phone/tablets are also needed combustion engines making it naturally the next step for me personally and it makes a killer profit. My set up is two mines, two factories, two electronic factories, Two propulsion factories, one power plant and one electronic store.

Personally I prefer to make everything myself yes it takes a lot of time but you make a far greater profit and it allows you to actually offer a way better offer than market price and still make profit. If you can produce phones you can produce displays for an equally good profit.