This is my first round playing this game and I just decided to post some thoughts about it.
First thing first, in a game with limited building space, the best way to maximize profit is to use space efficiently. I notice that industries are not equal. I don't mean stuff like car dealers are better than a textile shop, that's pretty obvious. What I mean is that even among the lv 0 shops (furniture, DIY, textile, toy, cafe, grocery, book), their profit per building space (which I will call pps) isn't equal either.
so to calculate pps
pps = ((norm price for 1 item*1.5)-production cost)/the combine space of all components
space = 1/production per building (at lv 0)
*note* shop space is not included in this equation
For example, the best lv 0 product a bookshop can produce is newspaper, standing at 15252 pps, while the best level 0 product a furniture shop can produce is a wooden table, standing at 18938 pps.
Also I notice there are 'trap products' with exceptionally low pps as well. For example, Christmas trees have 5084 pps, and motor oil have 5922 pps.
Here are the list of average PPS for the lv 0 shops
Textile = 23151
DIY = 21990
Furniture = 20451
Bookstore = 17790
Toyshop = 17632
Grocery = 10564
Cafe = 8788
Textile
pros = crocodile bags, low natural resource dependency
cons = too much other low pps items
although it does have the highest average pps, most of it comes from crocodile bags, standing at 1354500 pps. After getting to 35 R&D it is best to minimize down to just a few products (to maintain shop SV) and build as many crocodile bags as you can. Although there is the problem that car dealer is at 34 R&D, which mean this huge pps boost really isn't unique for textile manufacturers.
DIY
pros = uses wide range of resources, all around high pps
cons = none
This shop is perhaps the easiest to maintain and best overall. PPS is generally high except for Christmas trees and lumbers (which you can skip entirely).
Furniture
pros = easy to maintain, all around high pps
cons = uses too much lumber
This shop is limited by the amount of lumbers you have, making it not possible to just fill your map with them.
Bookstore
pros = easy to maintain, average pps, low competition
cons = use too much wood
This shop suffers the same problem as furniture, except with a lower pps. But at least you can be sure that the demand will remain relatively high.
Toy shop
pros = average pps, uses wide range of resources
cons = hard to maintain, moderate/high competition
I am not sure why so many people like this shop. It's pps is average, and the production numbers doesn't come together at all.
Grocery and Cafe
pros = hard to maintain, low pps
If you are looking for a challenge, then this is the way to go. Otherwise it's best to avoid them entirely.
As far as shops goes, it's upgrade is simply not worth it at a low R&D level. To calculate shop efficiency level
shop pps = (ratio*((1000*upgrade lv)+lv 0 upkeep of shop))-((ratio+1)*lv 0 upkeep of shop)
ratio = 1/((1.05^upgrade lv)-1))
note* rounding is not included in this equation, as this will take into consideration of individual items.
So for example, a lv 0 furniture shop at 0 R&D will have a 18000 pps compare to a lv 1 furniture shop, or 13901 pps compare to a lv 10 furniture shop. This is to say that, even excluding the huge upgrade cost, if you stay at level 0 and just build 1 more shop when needed, this shop is technically giving you a 18000 pps. Of course this ratio changes according to the cost of the shop, which is affected by what it is and the current R&D.
As far as QL goes, unless your intention is to set yourself up for next round, it's not worth the cost and effort. It simply cost too much to be pay back within the round that it is being utilized.
I will probably update this as I gather more information about this game.