I think starting with 3 boosted only factories is ok. Then you go up to 4 and then to 5 ... once having 5 you start seriously leveling, I think seriously leveling 3 of the boosted only factories would be enough, because later you get a boost on another/advanced factory type, so 3 from the first, 3 from the second, all well leveled should it do ... but we will see.
That's regarding to factory type/levels.
You should always produce the shortest possible production-time, best would be 3 hours (forget sleeping or work ...).
You start a couple of days producing and offering all what's over 100 of your boosted product on the trader. Don't make 'big offers', people need 3, 5, or 7 ... and even if they need 100, twenty offers with 5 are also hundred (and not more expensive ...).
When you reach this way 100 of the two not boosted products, you start offering all what's over 150 of your products on the trader, until all reaches 150 , next 200, 250 etc. etc.
If you have 'nice' numbers of all products you can act/buy whatever you want without waiting a long or endless time.
Logically, when you act/buy spending products, you should 'restart' your product-collection as described above ...
Surely it's not the only strategy, but it is a strategy which even works if you are not playing with diamonds/real money.
Best regards,
Extranjero