• Do the tutorial and follow through the small quests.
  
• Sell things at 75% margin from the store.
  
• Unless you need quick cash, sell from the store. Face-to-Face sales does not generate taxes.
  
• Tax is how you upgrade your town and utilities.
  
• Set Taxes as high as you are comfortable with. 5~50% (you should still be making some profit)
  
• Quick Grofit!

• Unlocks after 250 taxes paid.
  
• Do the quests it asks you to do.
  
• Try not to bother too much with food items as most of them are cheap at this point.
  
• With limited space, each item display should be selling higher value goods for higher taxes.
  
• Keep selling armor pieces, not food!

• Unlocks after 750 taxes paid.
  
• Close the shoppe for a moment
  
• Buy a bow, and town gates will open!
  
• More importantly, buy a pick.
  
• Explore! While at it, visit purple-tree infested elf-land and mine handful of blue crystals.
  
• Crystal values at 1k. with 75% margin, you will be selling at 1.75k (the best at this point).
  
• It takes a while for crystals to respawn, return to town for now, and come back later for more.
  
• Do not forget to close the shoppe when you go out to explore, unless you are okay with thieves. How generous!

• Unlocks after 1,200 taxes paid.
  
• There is a book on the shelf that will give 3 crafting recipes to alchemist.
  
• By now you will have some reputation points to spend. Open order window and go to unlock items.
  
• unlock a sword and wolf armor pieces, and sell them.
  
• Of course on 75% margin.

• Unlocked after 7,500 taxes paid.
  
• Close the shoppe!
  
• New hammer and broom can be found in the managerial house.
  
• Time to change furniture!
  
• Buy a single Trash Can. The thieves in disguise customers will pretend to be civilized and throw rubbish into the bin.
  
• Trash ought to be emptied once in a while. If you bought a chest from blacksmith, you can keep it there for gambling later. Or just put it in the grinder (no profit gained here).
  
• Time to use Shelf and Counters! Much more space efficient!
  
• You can either keep Pedestals and Tables in a chest or grind them.
  
• At this point, you can start two Ethereal quests : Dead Ethereal, and Ethereal Book.
  
• Do Dead Ethereal quest ASAP, it will expand your goods to sell (check the quest section below).
  
• After change of furniture and goods expansion, reopen and sell the new stuff at 75% margin still!
  
• New stuff : Runic Sword, Plate and Magelord armor sets.
  
• If you like fishing, Sir Shell sells green fishing rod, which lets you catch green quality fish.

• Unlocked after 12,000 taxes paid.
  
• Flies are gone!
  
• Talk to the chef for new recipe, and to hire 2 workers. They will boost daily income.
  
• Chris sells Thief Zapper Mk II for 50,000, and Helper Bot for 35,000.
  
• Helper Bot can be expanded outside managerial house to have 4 more for 20,000 each.
  
• Ruta sells Decorations. These will increase your shoppe's appeal.

• Unlocked after 21,000 taxes paid.
  
• Check Blacksmith for new recipes.
  
• Not much to see here. Keep selling Runic Sword and Plate & Magelord sets!

• Unlocked after 32,000 taxes paid.
  
• You can purchase Farm from Alchemist for 15,000. The farm is located outside the town.
  
• Farm comes with 1 plot. Maximum number of plots are 30 (29 additional for 8,000 each).
  
• Plants grow too slow to really bother for now.

• Unlocked after 50,000 taxes paid.
  
• Elf & Orc delivery bots will appear outside Managerial house.
  
• As you complete more Elf & Orc deliveries, up to 5 Elf & Orc items will unlock at their town.
  
• Delivery Bots arrive at 0800 (delivery item list resets), and leaves at 2200 in game time.
  
• You must submit a full list of items before bots depart at 2200. Partial delivery will have bots return with goods. At least you do not lose them.
  
• Some items are crafted and may not be able to to be completed within given day cycle. That's okay. Just do the easy deliveries.
  
• Elf & Orc items must be purchased in person at their town. Bring plenty of cash for bulk purchases.
  
• The people that were building things outside the town will have completed their outposts. The three families have arrived.
  
• Family representative at each location will sell 3 of their goods (9 new items).
  
• Of note is Squalo family's Fishing rod. If you like fishing. It lets you catch blue quality fish.
  
• Keep selling at 75% margin!
  

• Unlocked after 89,000 taxes paid.
  
• An inn is opened upstairs of tavern. Ethereal researchers take residence.
  
• Upon the first day cycle reset at 00:00 after upgrading, daily quest will be given by Kiki.
  
• Simply take the quest, and give her 10,000 for researching fund.
  
• Funding the research will unlock the Ethereal armor set in front of her.
  
• You need to do this daily quest total of 24 times for a full set unlock. Do it every day.
  
• Full Ethereal set will be required to proceed to Town Lv 4. Hence, investment.
  
• You may want to close the shoppe and sleep on bed to make time go by faster.

• Unlocked after 129,000 taxes paid.
  
• Your helper bots will now have flamethrowers on their arm.
  
• Bots will burn thieves if they come across them while working. It's an instant one shot kill.
  
• Bots will not actively seek out thieves.
  
• Your primary defense is still the Zapper Mk II and the weapon you have equipped.

• Unlocked after 169,000 taxes paid.
  
• Your Thief Zapper Mk II will now charge periodically for free!
  
• Of course it's your hard work and dedication, your investment, paying off.

• Unlocked after 450,000 taxes paid.
  
• Also should have Absorbed Ethereal (check below) and have 15% spawn rate of both Elf & Orc customers.
  
• If you have Elf & Orc goods displayed at your shoppe, Elves and Orcs will come. More display equals more of them up to 35% max for each race.
  
• You can check the current % of elves and orcs inside the managerial house on a chalkboard.
  
• By now you should be using mannequins to display full armor sets. Weapon racks for weapons.
  
  

• Unlocks after 750,000 taxes paid.
  
• You know the Trash bags you have been emptying out of your bin at the shoppe? If you have kept them, now you can shift through them by spending 250 per bag.
  
• Holding E key will open bags REALLY FAST. Watch your precious capital burn through.

• Unlocked after 1,100,000 taxes paid.
  
• Crafter costs are halved. If you have Management skill to cut half the costs, they work multiplicatively for a total of -75% the crafting cost.
  
• Enjoy your shoppe!

• Ethereal Book
  After Town Lv 2 unlock. Outside the town, visit the palisade with a tower, climb it, get "Ethereal Book" quest on top.
  Visit Sir Shell on top of a hill near Squalo family area. Talk to him.
  Jump into the nearby river and swim upstream.
  In the middle of the river's length, at the bottom, there's a chest with "Broken Truth" - End
  
• Dead Ethereal
  After Town Lv 2 unlock. Visit Selutarr family area, in front, there's an alter with bonfire.
  There is a dead ethereal, get the quest, Talk to Father Eduard to unlock Runic Sword.
  Talk to Sir Pennington to unlock Plate & Magelord armor sets. - End
  
• Absorbed Ethereal
  After Cook Lv 3 unlock and fully unlocking the Ethereal armor set from Kiki, equip the full set,
  Go through the purple portal near Elven village.
  Absorb the Ethereal. - End

Stop reading this, go play and have fun. But thank you for reading thus far.

Since you read all teh way down here, I'll write one last tip:
When upgrading shoppe's left and right wing upstairs, remove furniture and merchandises out of stair's way. Anything that was in the stair's way will be removed and will not be returned.
The stairs will form on the other sides of the central hall on the right and left wings. Keep those walls clean before upgrade.

I am the author of fandom wiki's following article for a quick glance:
https://shoppe-keep-2.fandom.com/wiki/Town_Progression#slideshow-0