Making Trading Block, setup like "Noppes Custom NPC traders" style

I can say myself as absolutely noob on this program, Im sick of asking some kind of mods to this and this, but no body cares so I decided if I try to make my own might be good I think, 

Hi guys anyone I neeed help Im planning to make a trading block that same as Noppes Custom NPC traders do, (really the same I hope so) but not a villiger instead it is a block or let me say a stall,

Im having trouble understanding too many instructions and procedures to create it in MCreator and cant find exact tutorial for this.

Please help me, 

What I want to change in that trader is i want  to put more slot for items to be trade and 4 slot for each item "for trade"

Heres my planned GUI for it I bet its very understandable...

It can be upgradable using configuration key which can also be included as a tool for creative setup and survival setup.

Creative setup=native setup of a trading block same setup of how you create the Noppes Custom NPC Traders on what items you like to trade and ovbiuosly in creative only.

Survival Setup= a player can set up a trader stall using survival configuration key but limited to only what materials is present in your inventory

Upgrading for it to have more page and slot for items to trade

But if you can make one please share it and inform me Thanks so much