A good trading hall is the backbone of any survival economy. The goal is to lock in productive trades and keep villagers safe and easy to access.
Start by building a central hall with individual 1x1 cells for each villager. Use a cell design that lets you hit the workstations while keeping villagers contained.
Place a fletching table for Fletcher, lectern for Librarian, smithing table for Toolsmith, and so on. Place and break the workstation repeatedly to reroll trades until you get the ones you want, then lock the trade by trading once.
Add a sorter system that routes finished goods — emeralds, enchanted books, iron — into chests automatically using hoppers.
Include an iron farm above the hall by placing multiple villagers with a zombie in eyesight to trigger golem spawns. Golems fall into a kill chamber below.
Finally, light up every surface so no mobs can spawn, and add slabs or carpets so golems (and other villagers) can't escape their designated areas.