TOM NOOK: SHOP PROGRESSION
The following are the expansions for Tom Nook's shop and how to obtain them:
Nook's Cranny: Available at start.
Nook 'n Go: Spend 25,000 Bells worth of merchandise.
Nookway: Spend 65,000 Bells worth of merchandise.
Nookingtons: Spend 240,000 Bells and have a visiting friend buy something from Nook. Note: This version of the store includes a hair salon.

TOME NOOK: SHOP POINT REWARDS
Buy as much as you can in Nook's shop. Not only will his selection get bigger, but you will get points for every purchase. Get enough purchases to become a member. Keep spending at Nook's shop to accumulate PIM points, and rewards at the following levels.
300 PIM points: Nook's Cranny model and store membership
3,000 PIM points: Nook' n Go model and 5% discount
10,000 PIM points: Nookway model and 10% discount
20,000 PIM points: Nookington's model and 20% Discount

TOM NOOK: GENERAL TIPS
How to restock the shop: Save your game and then go to your phone. Select "Reset Clock" and change the date. Nook will have all new furniture in his shop.
Bulletin board message: When you have to write the bulletin board message for Tom Nook, you can type just one letter and he will accept it to be there.