These guidelines are based on calculations. I compared the "Increased Hourly Gain/ Upgrading or Building Hours" and took the "Increased Hourly Gain" into consideration.
However this method is only a personal view and might ruin your fun for game if you just copy.
Castle is ignored. Gem buildings are not included in this guide.
First of all:
Build Cottage 1st
Upgrade Cottage 1st to lv2
Build Cottage 2nd
Upgrade Cottage 2nd to lv2
Then the same for Farm-> Bazaar -> Bakery in order.
Now the real thing comes:
If multiple actions are listed in one step, you could do it in any order you like.
Remember you could have 2 of each type of buildings. Get both done.
1) Upgrade Farm -> lv3
2) Upgrade Bazaar -> lv3
3) Build a Tavern, Build a Silo, Build a Library, Build a Tailor, Upgrade a Silo to lv2
4) Upgrade a Bakery -> lv3, Upgrade a Farm ->lv4
Upgrade Cottage as frequently as you like. Because an ordinary player is actually keeping Cottage idle for longer time than others, gain from Cottage is hard to measure.
Only from now it's safe to build any more advanced buildings asap after they are unlocked,
if you have sufficient cash flow.
5) Upgrade a Bazaar -> lv4, Upgrade a Silo -> lv3
6) Upgrade a Tailor -> lv2, Upgrade a Tavern -> lv2, Upgrade a Library -> lv2, Upgrade a Tailor -> lv 3, Upgrade a Stable -> lv2
7) Upgrade a Farm -> lv5, Upgrade a Silo -> lv4, Upgrade a Bazaar -> lv5, Upgrade a Bakery -> lv4
8) Upgrade a Leatherworker -> lv2, Upgrade a Tavern -> lv3, Upgrade a Cartographer -> lv2, Upgrade a Bakery -> lv5
From this point each step of upgrading takes too long (12 hours at least) , thus time management is more important than the guidelines from calculation.
9) Upgrade a Leatherworker -> lv3, Upgrade a Tailor -> lv4, Upgrade a Cartographer -> lv3
10) Upgrade Pottery Maker -> lv2, then take your time.