Example: i want to extract items from the furnace only if the output slot is full (max stack size), to be able to take a full stack out of the furnace myself getting all the exp. But in case the stack is full it should extract a single item in order to not to stop smelting items.
Instead it begins to extract an item as soon as there is an item since there are no free spaces left over.
Inventory Full check doesn't let me choose an item as argument (to check whether the inventory is full for a given item type) thus all stacks that the given item would fit in already have max size

It would need a lot of gate triggers to be able to do this properly, however I think it can be better solved with proper data stuff in BC8.

(Also because most of the gate triggers are for general inventory stuffs, I want to add fine-tuned controls)

maybe again way too general but what about impementing some drag & drop logic into the current gates? (input nodes, output nodes & basig logic gates(and/or/not))
Of course the drag & drop screen will be provided by any working table as assembly table, integration table and the zone planner are.
The "price" of the gate would determine how many nodes you can use. This would easen "and"/"or" and allow more complex stuff (like the not gate) while simplifying the needed nodes (no "has space" anymore since that's "not full" and vice versa)
One shouldn't allow cycles since these would lead to an infinite state change. The better option would be to add some input node that is triggered in the next cycle depending on the value of the previous cycle (ticks). This way you can make a simple "clock" similar you can do currently by setting redstone output if there is no redstone input but have no problems with the logic