i guess you could do it by adding a dark cable that gets activated when your furnace is working, thus preventing your system from inputting more items through the interface
That could be the first really useful idea here. 1) level emitter on export bus 2) export bus set to export one item at a time 3) dark cable turned off as soon as the machine is working. This will shut down the export bus so only one item enters the furnace at a time and as soon as the last item is smelted there is no need to export more. Brilliant! Now the problem is: How do I detect a working machine? The only way I know of is good old BC gates. So still no AE solution
I don't quite follow. Are you saying that you want for example 5 processors always in you inventory? If so, that is what a level emitter is for. It will emit a Redstone signal when a level has been met. I do find this cumbersome because there may not be enough room since level emitters o lyrics handle one item.
This works as long as the crafting is instant. Emitter turns on, item is crafted, emitter turns off. As soon as the crafting takes more than half the time between two checks of the emitter you will start producing more items than you took out of the system. This happens because the first crafting process has not yet ended when the emitter checks again, so another set of ressources is exported to the crafter. The overproduction increases dramatically with the time the crafter needs to craft one item only limited by the inventory space for raw materials (e.g. steam boiler: nine stacks - that's a damn lot of assemblies).
This is where you can get creative with item translocator. Take a chest and attach an ME storage bus set for extract only. Use a translocator between that chest and an ME Interface. Place the desired items to extract and or craft in the interaces's export config and specify the same object plus quantity in the filter of the Translocator. This will keep a specific quantity of 8 items stocked cleanly in your chest which is attached to your AE system.
I have a similar setup for Ender bags but not quite this. So this is untested.
This setup won't work because you'll get a circular reference. The interface will pull items from the chest via the storage bus. Interface needs to provide item and pulls it out of the chest, the translocator sees items missing in the chest and pulls one out of the interface. Now the interface is missing one item again and will pull it from the chest.
Only way to prevent that would be setting the interface to 'always craft'.
Now here's the old problem again: I haven't tested this yet, but I assume the interface will do cyclic checks just like the export bus/level emitter combo and will go into a crafting frenzy, too (see above).