It's a tad more complex than that
There is no 'round robin' or item splitting in LP and there is no need for that.
Items entering the system are routed based on priority:
1st: active requests (e.g. player request or supplier pipe)
2nd: passive requests (e.g. passive supplier module)
3rd: specified item sinks (item sink module or -pipe)
4th: polymorphic sinks
5th: basic pipes with filter
6th: terminus module
7th: default route
So the first valid target in your network is the storage. As long as it doesn't fill up, coal always will go there.
To provide coal to your furnace, put a supplier pipe on the chest near the furnace (or maybe directly on the furnace) and set it to any number of coal.
Additionally you have to add a provider module on the chassi pipes at your storage chests.
Whenever the number of coal in the furnace chest drops below the specified number in the supplier pipe, it'll request new coal from the storage.
That's not QUITE right. LP works on a dual system. Passive Routing (or Extraction/Sink) and Active Requesting
The first is likely the simpler of the two, as items entering the system (via extraction module or otherwise) will be routed pretty much as above. Bear in mind the Active Requestors do NOT get any priority here, they don't take part in this section.
The second involves the active requestors. Provider Pipes or modules act as the entrances to this part of LP, Crafting Pipes or Modules act as both Providers (for the item they craft) and Requestors (for the items they need to make it), and Request or Supplier Pipes, which actively pull from the providers.
For instance, if you request a bucket, a provider pipe will provide 3 iron to a crafting pipe, where the attached table crafts the bucket, which is then provided to the request pipe. This does mean that the supplier pipe will not receive items at all if there are no provider pipes/modules that can supply the pipe. This shouldn't be a problem if you are using at least a chassis mkII with the relevant sink module along with provider modules though.