Smithed crafting and custom blocks

https://smithed.dev/packs/GlsJvron3k5H2Z9Q5LHn
Rignchen suggested I use Smithed so I'm working my way through wrapping my head around what is happening in it and I would like to know what files I need to edit instead of digging through it all by hand.
I have found the recipes file that I can edit "datapacks\data\smithed.crafter\functions\v0.2.0\recipes\shaped.mcfunction" which then gives you the item at "datapacks\data\smithed.crafter\loot_tables\blocks(whatever I want the outcome).json"
I would like to understand how placing works with the furnace and CMD so that I can add in all the correct recipe outputs.
Basically, I need an explanation on this:
{CustomModelData:100000,display:{Name:'{"translate":"block.smithed.crafter","italic":false}'},BlockEntityTag:{Items:[{id:"minecraft:stone",Count:1b,Slot:0b,tag:{smithed:{block:{id:"smithed:crafter"}}}}]}}
why does the furnace need an item in a slot in the nbt?
do I need to attach my CMD to a Minecraft override of the furnace?
do I need to do anything with the block placing code or will it recognize the CMD I put into the recipe output?
do I have to do anything in general to get the pack placing into the world?
I have the smithed.custom_block but do I need to edit anything for it to work?