Just to reply in a general way, rather than replying to quotes...
Yes I agree about moving up some levels at least. That's why I chose toys, in fact, and I've just begun making my first furry pets.
However, I've also begun quality research for some of the basic materials. I'll soon be at 100 buildings...just keeping a few slots open for petrochemicals for my plastic dolls. I'm keeping about 8 million in the kitty when offline for long in case I stop selling due to price drops. This has happened before.
Since reading what Morgie wrote, though, I'm also running furniture and DIY stores and even a grocery. That's apart from my focus on toy shops and cafes. The furniture and DIY businesses are very painful to run. Purchasing is difficult, they only barely make any money, and sales often drop. I'm keeping going with toys, but only by adding an extra shop (4 total), which spreads out the sales a bit, I also switched one of the toy plants making wooden locos to make furry pets, instead of building a new one.
I then started a small wine business using some of my glass and this helps feed the grocery. Otherwise I just buy eggs, meat and other things from market.
Overall, the cafes do very well, and marbles do better now relative to tricycles which are rather soft in off-season.
Kahla: "But even so, the supply is continuously changing as people drop or take up production of that product." Very true! You can see the difference when our friends from Germany come online!
On one occassion I simply stopped selling those wooden ladders. Don't know what happened. Did they all go in and reduce their own prices? 
I'm not too worried. I have the money to jump more levels if I need to. But what I meant is, I won't jump too high just for the sake of it. I feel that I should only jump once I have a specific target in mind. For example, I only want to jump to pushcarts when I have mastered "petrochemicals" for plastic dolls, and so on.
Morgie, my company is Afroco. (...I'm from South Africa =) ) Now I don't expect to do well in the highscores, but I'm reasonably pleased to be in the upper 100 for ROI and suchlike. Those are the efficiencies I was concentrating on. However, as you can see, for Best Vendor I'm still down at 2597! I'm sure that's below many who aren't even actively playing. In other words, I incur negative penalties.
It is this penalty I don't really understand. So then my overall score is 667.